Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions from 5 to 16.

Since 1950 the world ______ nearly one-fifth of the soil from its agricultural land and one-fifth of its tropical forests.

A. has lost   

B. lost          

C. was losing         

D. had been lost

Read the following passage and then choose the word (A, B, C or D) that best completes each blank. 

There’s much more water than land on the ….(36)… of the earth. The seas and oceans cover nearly four-fifth of the whole world, and only one-fifth of land. If you traveled over the earth in different directions, you would have to spend much more of your time …(37)… on water than on roads or railways. We sometimes forget that for every mile of land there is four miles of water. There’s so much water in the surface of our earth that we ....(38)… to use two words to describe. We use the word SEAS .....(39)... those parts of water surface which has only few hundreds of mile, the word OCEANS to describe the huge area of water which are thousands of miles wide and very deep.

Câu 36:                                  A. cover                    B. surface                 C. outer       D. outside

Câu 37:                                  A. to move                B. move                    C. moved     D. moving

Câu 38:                                  A. must                     B. should                  C. have        D. would

Câu 39:                                  A. describing             B. describes              C. describe   D. to describe

Earth is losing wildlife at a faster rate than at any time in history. This is according to the new "Living Planet Report" from the World Wildlife Fund. The report says the global wildlife population shrank by 60 per cent between 1970 and 2014. The WWF warned that: "Earth is losing biodiversity at a rate seen only during mass extinctions." Researchers state that most of the decline in our animal population is because of "exploding human consumption". There are more and more humans on this planet. We are eating more, overfishing, cutting down trees for beef production, consuming more, and using more energy and natural resources. This has resulted in a massive loss of habitat for animals.The report estimates that only a quarter of the world's land has been untouched by humans. This means human activity has greatly affected animals on three-quarters of Earth's surface. Researchers tracked more than 4,000 species of mammals, birds, reptiles, fish and amphibians. They say the loss of animal life is worst in South and Central America. These regions saw an 89 per cent loss in the population of vertebrates in the past four decades. The WWF wrote: "The astonishing decline in wildlife population...is a [depressing] reminder, and perhaps the ultimate indicator, of the pressure we [put] on the planet." It warned: "We can be the generation that had its chance and failed to act; that let Earth slip away."

(ANswer the question )

1 what is the name of there port from the wwf

2 what did the WWF say the earth is losing at a rae seen in extinction

3 what did researchers say the decide in wildlife was because of

4 what the article say trees were being cut down for

5 what did the article say animals had lost

minh cam on nhieu nha

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 35 to 42.

        Desertification is the degradation of once-productive land into unproductive or poorly productive land. Since the first great urban-agricultural centers in Mesopotamia nearly 6,000 years ago, human activity has had a destructive impact on soil quality, leading to gradual desertification in virtually every area of the world.

        It is a common misconception that desertification is caused by droughts. Although drought does make land more vulnerable, well-managed land can survive droughts and recover, even in arid regions. Another mistaken belief is that the process occurs only along the edges of deserts. In fact, it may take place in any arid or semiarid region, especially where poor land management is practised. Most vulnerable, however, are the transitional zones between deserts and arable land; wherever human activity leads to land abuse in these fragile marginal areas, soil destruction is inevitable.

        Agriculture and overgrazing are the two major sources of desertification. Large-scale farming requires extensive irrigation, which ultimately destroys lands by depleting its nutrients and leaching minerals into the topsoil. Grazing is especially destructive to land because, in addition to depleting cover vegetation, herds of grazing mammals also trample the fine organic particles of the topsoil, leading to soil compaction and erosion. It takes about 500 years for the earth to build up 3 centimeters of topsoil. However, cattle ranching and agriculture can deplete as much as 2 to 3 centimeters of topsoil every 25 years- 60 to 80 times faster than it can be replaced by nature.

        Salinization is a type of land degradation that involves an increase in the salt content of the soil. This usually occurs as a result of improper irrigation practices. The greatest Mesopotamian empires- Sumer, Akkad and Babylon- were built on the surplus of the enormously productive soil of the ancient Tigris-Euphrates alluvial plain. After nearly a thousand years of intensive cultivation, land quality was in evident decline. In response, around 2800 BC the Sumerians began digging the huge Tigris-Euphrates canal system to irrigate the exhausted soil. A temporary gain in crop yield was achieved in this way, but over-irrigation was to have serious and unforeseen consequences. From as early as 2400 BC we find Sumerian documents referring to salinization as a soil problem. It is believed that the fall of the Akkadian Empire around 2150 BC may have been due to a catastrophic failure in land productivity; the soil was literally turned into salt. Even today, four thousand years later, vast tracks of salinized land between the Tigris and Euphrates rivers still resemble rock-hard fields of snow.

        Soil erosion is another form of desertification. It is a self-reinforcing process; once the cycle of degradation begins, conditions are set for continual deterioration. As the vegetative cover begins to disappear, soil becomes more vulnerable to raindrop impact. Water runs off instead of soaking in to provide moisture for plans. This further diminishes plan cover by leaching away nutrients from the soil. As soil quality declines and runoff is increased, floods become more frequent and more severe. Flooding washes away topsoil, the thin, rich, uppermost layer of the earth’s soil, and leaves finer underlying particles more vulnerable to wind erosion. Topsoil contains the earth’s greatest concentration of organic matter and microorganisms, and is where most of the earth’s land-based biological activity occurs. Without this fragile coat of nutrient-laden material, plan life cannot exist. An extreme case of its erosion is found in the Sahel, a transitional zone between the Sahara Desert and the tropical African rain forests; home to some 56 million people. Overpopulation and overgrazing have opened the hyperarid land to wind erosion, which is stripping away the protective margin of the Sahel, and causing the desert to grow at an alarming rate. Between 1950 and 1975, the Sahara Desert spread 100 kilometers southward through the Sahel.

Paragraph 4 of the passage serves mainly to do which of the following?

A. Propose a method for dealing with the desertification problem. 

B. Describe the main cause of desertification in one particular area 

C. Describe one process that leads to desertification 

D. Show the progress of desertification down through history

Read  the  following  passage  and  mark  the  letter  A,  B,  C,  or  D  on  your  answer  sheet  to  indicate  the  correct answer to each of the questions from 36 to 42. 

DESERTIFICATION

Desertification is the degradation of once-productive land into unproductive or poorly productive land. Since the first great urban-agricultural centers in Mesopotamia nearly 6,000 years ago, human activity has had a destructive impact on soil quality, leading to gradual desertification in virtually every area of the world. 

It is a common misconception that desertification is caused by droughts. Although drought does make land  more  vulnerable,  well-managed  land  can  survive  droughts  and  recover,  even  in  arid  regions.  Another mistaken belief is that the process occurs only along the edges of deserts. In fact, it may take place in any arid or  semiarid  region,  especially  where  poor  land  management  is  practiced.  Most  vulnerable,  however,  are  the transitional  zones  between  deserts  and  arable  land;  wherever  human  activity  leads  to  land  abuse  in  these fragile marginal areas, soil destruction is inevitable. 

[1]  Agriculture  and  overgrazing  are  the  two  major  sources  of  desertification.  [2]  Large-scale  farming requires  extensive  irrigation,  which  ultimately  destroys  lands  by  depleting  its  nutrients  and  leaching  minerals into the topsoil. [3] Grazing is especially destructive to land because, in addition to depleting cover vegetation, herds of grazing mammals also trample the fine organic particles of the topsoil, leading to soil compaction and

erosion. [4] It takes about 500 years for the earth to build up 3 centimeters of topsoil. However, cattle ranching and agriculture can deplete as much as 2 to 3 centimeters of topsoil every 25 years - 60 to 80 times faster than it can be replaced by nature. 

Salination  is  a  type  of  land  degradation  that  involves  an  increase  in  the  salt  content  of  the  soil.  This usually occurs as a result of improper irrigation practices. The greatest Mesopotamian empires- Sumer, Akkad and  Babylon-  were  built  on  the  surplus  of  the  enormously  productive  soil  of  the  ancient  Tigris-  Euphrates alluvial  plain.  After  nearly  a  thousand  years  of  intensive  cultivation,  land  quality  was  in  evident  decline.  In response, around 2800 BC the Sumerians began digging the huge Tigris-Euphrates canal system to irrigate the exhausted soil. A temporary gain in crop yield was achieved in this way, but over-irrigation was to have serious and unforeseen consequences. From as early as 2400 BC we find Sumerian documents referring to salinization as a soil problem. It is believed that the fall of the Akkadian Empire around 2150 BC may have been due to a catastrophic failure in land productivity; the soil was literally turned into salt. Even today, four thousand years later,  vast  tracks  of  salinized  land  between  the  Tigris  and  Euphrates  rivers  still  resemble  rock-hard  fields  of snow.

Soil  erosion  is  another  form  of  desertification.  It  is  a  self-reinforcing  process;  once  the  cycle  of degradation begins, conditions are set for continual deterioration. As the vegetative cover begins to disappear, soil becomes more vulnerable to raindrop impact. Water runs off instead of soaking in to provide moisture for plans. This further diminishes plan cover by leaching away nutrients from the soil. As soil quality declines and runoff  is  increased,  floods  become  more  frequent  and  more  severe.  Flooding  washes  away  topsoil,  the  thin, rich, uppermost layer of the earth’s soil, and leaves finer underlying particles more vulnerable to wind erosion. Topsoil contains the earth’s greatest concentration of organic matter and microorganisms, and is where most of the earth’s land-based biological activity  occurs.  Without this fragile  coat of nutrient-laden material, plan life cannot exist. An extreme case of its erosion is found in the Sahel, a transitional zone between the Sahara Desert and  the  tropical  African  rain  forests;  home  to  some  56  million  people.  Overpopulation  and  overgrazing  have opened  the  hyperarid  land  to  wind  erosion,  which  is  stripping  away  the  protective  margin  of  the  Sahel,  and causing  the  desert  to  grow  at  an  alarming  rate.  Between  1950  and  1975,  the  Sahara  Desert  spread  100 kilometers southward through the Sahel. 

Paragraph 4 of the passage serves mainly to do which of the following?

A. Show the progress of desertification down through history.

B. Propose a method for dealing with the desertification problem.

C. Describe one progress that leads to desertification.

D. Describe the main cause of desertification in one particular area.

Read  the  following  passage  and  mark  the  letter  A,  B,  C,  or  D  on  your  answer  sheet  to  indicate  the  correct answer to each of the questions from 36 to 42. 

DESERTIFICATION

Desertification is the degradation of once-productive land into unproductive or poorly productive land. Since the first great urban-agricultural centers in Mesopotamia nearly 6,000 years ago, human activity has had a destructive impact on soil quality, leading to gradual desertification in virtually every area of the world. 

It is a common misconception that desertification is caused by droughts. Although drought does make land  more  vulnerable,  well-managed  land  can  survive  droughts  and  recover,  even  in  arid  regions.  Another mistaken belief is that the process occurs only along the edges of deserts. In fact, it may take place in any arid or  semiarid  region,  especially  where  poor  land  management  is  practiced.  Most  vulnerable,  however,  are  the transitional  zones  between  deserts  and  arable  land;  wherever  human  activity  leads  to  land  abuse  in  these fragile marginal areas, soil destruction is inevitable. 

[1]  Agriculture  and  overgrazing  are  the  two  major  sources  of  desertification.  [2]  Large-scale  farming requires  extensive  irrigation,  which  ultimately  destroys  lands  by  depleting  its  nutrients  and  leaching  minerals into the topsoil. [3] Grazing is especially destructive to land because, in addition to depleting cover vegetation, herds of grazing mammals also trample the fine organic particles of the topsoil, leading to soil compaction and

erosion. [4] It takes about 500 years for the earth to build up 3 centimeters of topsoil. However, cattle ranching and agriculture can deplete as much as 2 to 3 centimeters of topsoil every 25 years - 60 to 80 times faster than it can be replaced by nature. 

Salination  is  a  type  of  land  degradation  that  involves  an  increase  in  the  salt  content  of  the  soil.  This usually occurs as a result of improper irrigation practices. The greatest Mesopotamian empires- Sumer, Akkad and  Babylon-  were  built  on  the  surplus  of  the  enormously  productive  soil  of  the  ancient  Tigris-  Euphrates alluvial  plain.  After  nearly  a  thousand  years  of  intensive  cultivation,  land  quality  was  in  evident  decline.  In response, around 2800 BC the Sumerians began digging the huge Tigris-Euphrates canal system to irrigate the exhausted soil. A temporary gain in crop yield was achieved in this way, but over-irrigation was to have serious and unforeseen consequences. From as early as 2400 BC we find Sumerian documents referring to salinization as a soil problem. It is believed that the fall of the Akkadian Empire around 2150 BC may have been due to a catastrophic failure in land productivity; the soil was literally turned into salt. Even today, four thousand years later,  vast  tracks  of  salinized  land  between  the  Tigris  and  Euphrates  rivers  still  resemble  rock-hard  fields  of snow.

Soil  erosion  is  another  form  of  desertification.  It  is  a  self-reinforcing  process;  once  the  cycle  of degradation begins, conditions are set for continual deterioration. As the vegetative cover begins to disappear, soil becomes more vulnerable to raindrop impact. Water runs off instead of soaking in to provide moisture for plans. This further diminishes plan cover by leaching away nutrients from the soil. As soil quality declines and runoff  is  increased,  floods  become  more  frequent  and  more  severe.  Flooding  washes  away  topsoil,  the  thin, rich, uppermost layer of the earth’s soil, and leaves finer underlying particles more vulnerable to wind erosion. Topsoil contains the earth’s greatest concentration of organic matter and microorganisms, and is where most of the earth’s land-based biological activity  occurs.  Without this fragile  coat of nutrient-laden material, plan life cannot exist. An extreme case of its erosion is found in the Sahel, a transitional zone between the Sahara Desert and  the  tropical  African  rain  forests;  home  to  some  56  million  people.  Overpopulation  and  overgrazing  have opened  the  hyperarid  land  to  wind  erosion,  which  is  stripping  away  the  protective  margin  of  the  Sahel,  and causing  the  desert  to  grow  at  an  alarming  rate.  Between  1950  and  1975,  the  Sahara  Desert  spread  100 kilometers southward through the Sahel. 

Which of the following statement is true about desertification?

A. It has a history as long as that of civilization.

B. It was just as serious in the past as it is today.

C. It is a fairy recent problem.

D. Ancient societies managed the problem well.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 35 to 42.

        Desertification is the degradation of once-productive land into unproductive or poorly productive land. Since the first great urban-agricultural centers in Mesopotamia nearly 6,000 years ago, human activity has had a destructive impact on soil quality, leading to gradual desertification in virtually every area of the world.

        It is a common misconception that desertification is caused by droughts. Although drought does make land more vulnerable, well-managed land can survive droughts and recover, even in arid regions. Another mistaken belief is that the process occurs only along the edges of deserts. In fact, it may take place in any arid or semiarid region, especially where poor land management is practised. Most vulnerable, however, are the transitional zones between deserts and arable land; wherever human activity leads to land abuse in these fragile marginal areas, soil destruction is inevitable.

        Agriculture and overgrazing are the two major sources of desertification. Large-scale farming requires extensive irrigation, which ultimately destroys lands by depleting its nutrients and leaching minerals into the topsoil. Grazing is especially destructive to land because, in addition to depleting cover vegetation, herds of grazing mammals also trample the fine organic particles of the topsoil, leading to soil compaction and erosion. It takes about 500 years for the earth to build up 3 centimeters of topsoil. However, cattle ranching and agriculture can deplete as much as 2 to 3 centimeters of topsoil every 25 years- 60 to 80 times faster than it can be replaced by nature.

        Salinization is a type of land degradation that involves an increase in the salt content of the soil. This usually occurs as a result of improper irrigation practices. The greatest Mesopotamian empires- Sumer, Akkad and Babylon- were built on the surplus of the enormously productive soil of the ancient Tigris-Euphrates alluvial plain. After nearly a thousand years of intensive cultivation, land quality was in evident decline. In response, around 2800 BC the Sumerians began digging the huge Tigris-Euphrates canal system to irrigate the exhausted soil. A temporary gain in crop yield was achieved in this way, but over-irrigation was to have serious and unforeseen consequences. From as early as 2400 BC we find Sumerian documents referring to salinization as a soil problem. It is believed that the fall of the Akkadian Empire around 2150 BC may have been due to a catastrophic failure in land productivity; the soil was literally turned into salt. Even today, four thousand years later, vast tracks of salinized land between the Tigris and Euphrates rivers still resemble rock-hard fields of snow.

        Soil erosion is another form of desertification. It is a self-reinforcing process; once the cycle of degradation begins, conditions are set for continual deterioration. As the vegetative cover begins to disappear, soil becomes more vulnerable to raindrop impact. Water runs off instead of soaking in to provide moisture for plans. This further diminishes plan cover by leaching away nutrients from the soil. As soil quality declines and runoff is increased, floods become more frequent and more severe. Flooding washes away topsoil, the thin, rich, uppermost layer of the earth’s soil, and leaves finer underlying particles more vulnerable to wind erosion. Topsoil contains the earth’s greatest concentration of organic matter and microorganisms, and is where most of the earth’s land-based biological activity occurs. Without this fragile coat of nutrient-laden material, plan life cannot exist. An extreme case of its erosion is found in the Sahel, a transitional zone between the Sahara Desert and the tropical African rain forests; home to some 56 million people. Overpopulation and overgrazing have opened the hyperarid land to wind erosion, which is stripping away the protective margin of the Sahel, and causing the desert to grow at an alarming rate. Between 1950 and 1975, the Sahara Desert spread 100 kilometers southward through the Sahel.

According to the passage, many people’s understanding of desertification is incorrect because _________.

A. they do not see it as being caused by human activity 

B. they see it as being reversible 

C. they think of it as a very slow process 

D. they do not think of it as a serious problem

Read  the  following  passage  and  mark  the  letter  A,  B,  C,  or  D  on  your  answer  sheet  to  indicate  the  correct answer to each of the questions from 36 to 42. 

DESERTIFICATION

Desertification is the degradation of once-productive land into unproductive or poorly productive land. Since the first great urban-agricultural centers in Mesopotamia nearly 6,000 years ago, human activity has had a destructive impact on soil quality, leading to gradual desertification in virtually every area of the world. 

It is a common misconception that desertification is caused by droughts. Although drought does make land  more  vulnerable,  well-managed  land  can  survive  droughts  and  recover,  even  in  arid  regions.  Another mistaken belief is that the process occurs only along the edges of deserts. In fact, it may take place in any arid or  semiarid  region,  especially  where  poor  land  management  is  practiced.  Most  vulnerable,  however,  are  the transitional  zones  between  deserts  and  arable  land;  wherever  human  activity  leads  to  land  abuse  in  these fragile marginal areas, soil destruction is inevitable. 

[1]  Agriculture  and  overgrazing  are  the  two  major  sources  of  desertification.  [2]  Large-scale  farming requires  extensive  irrigation,  which  ultimately  destroys  lands  by  depleting  its  nutrients  and  leaching  minerals into the topsoil. [3] Grazing is especially destructive to land because, in addition to depleting cover vegetation, herds of grazing mammals also trample the fine organic particles of the topsoil, leading to soil compaction and

erosion. [4] It takes about 500 years for the earth to build up 3 centimeters of topsoil. However, cattle ranching and agriculture can deplete as much as 2 to 3 centimeters of topsoil every 25 years - 60 to 80 times faster than it can be replaced by nature. 

Salination  is  a  type  of  land  degradation  that  involves  an  increase  in  the  salt  content  of  the  soil.  This usually occurs as a result of improper irrigation practices. The greatest Mesopotamian empires- Sumer, Akkad and  Babylon-  were  built  on  the  surplus  of  the  enormously  productive  soil  of  the  ancient  Tigris-  Euphrates alluvial  plain.  After  nearly  a  thousand  years  of  intensive  cultivation,  land  quality  was  in  evident  decline.  In response, around 2800 BC the Sumerians began digging the huge Tigris-Euphrates canal system to irrigate the exhausted soil. A temporary gain in crop yield was achieved in this way, but over-irrigation was to have serious and unforeseen consequences. From as early as 2400 BC we find Sumerian documents referring to salinization as a soil problem. It is believed that the fall of the Akkadian Empire around 2150 BC may have been due to a catastrophic failure in land productivity; the soil was literally turned into salt. Even today, four thousand years later,  vast  tracks  of  salinized  land  between  the  Tigris  and  Euphrates  rivers  still  resemble  rock-hard  fields  of snow.

Soil  erosion  is  another  form  of  desertification.  It  is  a  self-reinforcing  process;  once  the  cycle  of degradation begins, conditions are set for continual deterioration. As the vegetative cover begins to disappear, soil becomes more vulnerable to raindrop impact. Water runs off instead of soaking in to provide moisture for plans. This further diminishes plan cover by leaching away nutrients from the soil. As soil quality declines and runoff  is  increased,  floods  become  more  frequent  and  more  severe.  Flooding  washes  away  topsoil,  the  thin, rich, uppermost layer of the earth’s soil, and leaves finer underlying particles more vulnerable to wind erosion. Topsoil contains the earth’s greatest concentration of organic matter and microorganisms, and is where most of the earth’s land-based biological activity  occurs.  Without this fragile  coat of nutrient-laden material, plan life cannot exist. An extreme case of its erosion is found in the Sahel, a transitional zone between the Sahara Desert and  the  tropical  African  rain  forests;  home  to  some  56  million  people.  Overpopulation  and  overgrazing  have opened  the  hyperarid  land  to  wind  erosion,  which  is  stripping  away  the  protective  margin  of  the  Sahel,  and causing  the  desert  to  grow  at  an  alarming  rate.  Between  1950  and  1975,  the  Sahara  Desert  spread  100 kilometers southward through the Sahel. 

According to the passage, many people’s understanding of desertification is incorrect because _____.

A. they do not think of of it as a serious problem

B. they see it as being reversible

C. they do not see it as being caused by human activity

D. they think of it as a very slow process

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 35 to 42.

        Desertification is the degradation of once-productive land into unproductive or poorly productive land. Since the first great urban-agricultural centers in Mesopotamia nearly 6,000 years ago, human activity has had a destructive impact on soil quality, leading to gradual desertification in virtually every area of the world.

        It is a common misconception that desertification is caused by droughts. Although drought does make land more vulnerable, well-managed land can survive droughts and recover, even in arid regions. Another mistaken belief is that the process occurs only along the edges of deserts. In fact, it may take place in any arid or semiarid region, especially where poor land management is practised. Most vulnerable, however, are the transitional zones between deserts and arable land; wherever human activity leads to land abuse in these fragile marginal areas, soil destruction is inevitable.

        Agriculture and overgrazing are the two major sources of desertification. Large-scale farming requires extensive irrigation, which ultimately destroys lands by depleting its nutrients and leaching minerals into the topsoil. Grazing is especially destructive to land because, in addition to depleting cover vegetation, herds of grazing mammals also trample the fine organic particles of the topsoil, leading to soil compaction and erosion. It takes about 500 years for the earth to build up 3 centimeters of topsoil. However, cattle ranching and agriculture can deplete as much as 2 to 3 centimeters of topsoil every 25 years- 60 to 80 times faster than it can be replaced by nature.

        Salinization is a type of land degradation that involves an increase in the salt content of the soil. This usually occurs as a result of improper irrigation practices. The greatest Mesopotamian empires- Sumer, Akkad and Babylon- were built on the surplus of the enormously productive soil of the ancient Tigris-Euphrates alluvial plain. After nearly a thousand years of intensive cultivation, land quality was in evident decline. In response, around 2800 BC the Sumerians began digging the huge Tigris-Euphrates canal system to irrigate the exhausted soil. A temporary gain in crop yield was achieved in this way, but over-irrigation was to have serious and unforeseen consequences. From as early as 2400 BC we find Sumerian documents referring to salinization as a soil problem. It is believed that the fall of the Akkadian Empire around 2150 BC may have been due to a catastrophic failure in land productivity; the soil was literally turned into salt. Even today, four thousand years later, vast tracks of salinized land between the Tigris and Euphrates rivers still resemble rock-hard fields of snow.

        Soil erosion is another form of desertification. It is a self-reinforcing process; once the cycle of degradation begins, conditions are set for continual deterioration. As the vegetative cover begins to disappear, soil becomes more vulnerable to raindrop impact. Water runs off instead of soaking in to provide moisture for plans. This further diminishes plan cover by leaching away nutrients from the soil. As soil quality declines and runoff is increased, floods become more frequent and more severe. Flooding washes away topsoil, the thin, rich, uppermost layer of the earth’s soil, and leaves finer underlying particles more vulnerable to wind erosion. Topsoil contains the earth’s greatest concentration of organic matter and microorganisms, and is where most of the earth’s land-based biological activity occurs. Without this fragile coat of nutrient-laden material, plan life cannot exist. An extreme case of its erosion is found in the Sahel, a transitional zone between the Sahara Desert and the tropical African rain forests; home to some 56 million people. Overpopulation and overgrazing have opened the hyperarid land to wind erosion, which is stripping away the protective margin of the Sahel, and causing the desert to grow at an alarming rate. Between 1950 and 1975, the Sahara Desert spread 100 kilometers southward through the Sahel.

Which of the following statements is true about desertification?

A. It was just as serious in the past as it is today. 

B. Ancient societies managed the problem well. 

C. It is a fairly recent problem. 

D. It has a history as long as that of civilization.