Cho m gam Fe tác dụng với dung dịch HCl dư thu được 1,12 lít khí H₂ (đktc). Giá trị của m là

A. 5,6

B. 1,12

C. 2,8

D. 1,4

Amino axit T no, mạch hở, có công thức phân tử C_nH_mO₄N, trong đó có tỉ lệ khối lượng m_C : m_N = 24 : 7. Giá trị của n và m lần lượt là

A. 4 và 7

B. 4 và 9

C. 5 và 9

D. 5 và 11

Các nước châu Phi cần có những giải pháp gì để khắc phục khó khăn trong quá trình khai thác, bảo vệ tự nhiên?

Quan sát hình 21.1b, hãy mô tả cách chọn chiều cao của êtô

Em có nhận xét gì về lưỡi cưa gỗ và lưỡi cưa kim loại? Giải thích sự khác nhau giữa 2 lưỡi cưa

Nêu công dụng của các dụng cụ gia công

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 28 to 34.

        Though Edmund Halley was very famous because of his achievements as an astronomer, he was a scientist of diverse interests and great skill. In addition to studying the skies, Halley was also deeply interested in exploring the unknown depths of the oceans. One of his lesser-known accomplishments that were quite remarkable was his design for a diving bell that facilitated exploration of the watery depths.

        The diving bell that Halley designed had a major advantage over the diving bells that were in use prior to his. Earlier diving bells could only make use of the air contained within the bell itself, so divers had to surface when the air inside the bell ran low. Halley’s bell was an improvement in that its design allowed for an additional supply of fresh air that enabled a crew of divers to remain underwater for several hours.

        The diving contraption that Halley designed was in the shape of a bell that measured three feet across the top and five feet across the bottom and could hold several divers comfortably; it was open at the bottom so that divers could swim in and out at will. The bell was built of wood, which was first heavily tarred to make it water repellent and was then covered with a half-ton sheet of lead to make the bell heavy enough to sink in water. The bell shape held air inside for the divers to breathe as the bell sank to the bottom.

        The air inside the bell was not the only source of air for the divers to breathe, and it was this improvement that made Halley’s bell superior to its predecessors. In addition to the air already in the bell, air was also supplied to the divers from a lead barrel that was lowered to the ocean floor close to the bell itself. Air flowed through a leather pipe from the lead barrel on the ocean floor to the bell. The diver could breathe the air from a position inside the bell, or he could move around outside the bell wearing a diving suit that consisted of a lead bell-shaped helmet with a glass viewing window and a leather body suit, with a leather pipe carrying fresh air from the diving bell to the helmet.

How long could divers stay underwater in Halley’s bell?

A. Only a few minutes

B. Just a few seconds 

C. For hours at a time

D. For days on end

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 28 to 34.

        Though Edmund Halley was very famous because of his achievements as an astronomer, he was a scientist of diverse interests and great skill. In addition to studying the skies, Halley was also deeply interested in exploring the unknown depths of the oceans. One of his lesser-known accomplishments that were quite remarkable was his design for a diving bell that facilitated exploration of the watery depths.

        The diving bell that Halley designed had a major advantage over the diving bells that were in use prior to his. Earlier diving bells could only make use of the air contained within the bell itself, so divers had to surface when the air inside the bell ran low. Halley’s bell was an improvement in that its design allowed for an additional supply of fresh air that enabled a crew of divers to remain underwater for several hours.

        The diving contraption that Halley designed was in the shape of a bell that measured three feet across the top and five feet across the bottom and could hold several divers comfortably; it was open at the bottom so that divers could swim in and out at will. The bell was built of wood, which was first heavily tarred to make it water repellent and was then covered with a half-ton sheet of lead to make the bell heavy enough to sink in water. The bell shape held air inside for the divers to breathe as the bell sank to the bottom.

        The air inside the bell was not the only source of air for the divers to breathe, and it was this improvement that made Halley’s bell superior to its predecessors. In addition to the air already in the bell, air was also supplied to the divers from a lead barrel that was lowered to the ocean floor close to the bell itself. Air flowed through a leather pipe from the lead barrel on the ocean floor to the bell. The diver could breathe the air from a position inside the bell, or he could move around outside the bell wearing a diving suit that consisted of a lead bell-shaped helmet with a glass viewing window and a leather body suit, with a leather pipe carrying fresh air from the diving bell to the helmet.

The subject of the preceding passage was most likely Halley’s _________.

A. childhood

B. invention of the diving bell 

C. work as an astronomer

D. many different interests

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 43 to 50.

It can be shown in facts and figures that cycling is the cheapest, most convenient, and most environmentally desirable term of transport in towns, but such cold calculations do not mean much on a frosty winter morning. The real appeal of cycling is that it is so enjoyable. It has none of the difficulties and tensions of other ways of traveling so you are more cheerful after a ride, even though the rush hour.

The first thing a non-cyclist says to you is: "But isn't it terribly dangerous?" It would be foolish to deny the danger of sharing the road with motor vehicles and it must be admitted that there are an alarming number of accidents involving cyclists. However, although police records indicate that the car driver is often to blame, the answer lies with the cyclist. It is possible to ride in such a way as to reduce risks to a minimum.

If you decide to join the thousands in Britain who are now returning to cycling as a cheap, satisfying form of transport your first problem will be trying to decide what bike to buy. Here are three simple rules for buying a bike:

1. Always buy the best you can afford. Of course there has to be a meeting point between what you would really like and economic reality, but aim as high as you can and you will get the benefit not only when you ride but also if you want to sell. Well-made bikes keep the value very well. And don't forget to include in your calculations the fact that you'll begin saving money on

fares and petrol the minute you leave the shop.

2. Get the best frame, the main structure of the bicycle, for your money as you can. Cheap brakes, wheels or gears can easily be replaced by more expensive ones, but the frame sets the upper limit on any transformation. You should allow for the possibility our cycling ambitions will grow with practice. When you begin, the four miles to work may the most you ever dream of, but after a few months a Sunday ride into the country begins to look more and more desirable. The best thing is to buy a bike just a little bit better than you think you'll need, and then grow into it. Otherwise, try to get a model that can be improved.

3.The fit is vital. Handlebars and seat height can be adjusted but you must get the right sized frame. On the whole it is best to get the largest size you can manage. Frame sizes are measured in inches and the usual adult range is from 21 inches to 25 inches, though extreme sizes outside those measurements can be found. Some people say if you take four inches off from your inside leg measurement you will end up with the right size of bike. The basic principle though is that you should be able to stand with legs either side of the crossbar (the bar that goes from the handlebars to the seat) with both feet comfortably flat on the ground.

Question 48: After you have been cycling for a few months the author suggests that you will _______.

A. want to ride only at weekends

B. want to ride further than you first imagined

C. find riding to work every day boring

D. find cycling in towns less dangerous

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 43 to 50.

It can be shown in facts and figures that cycling is the cheapest, most convenient, and most environmentally desirable term of transport in towns, but such cold calculations do not mean much on a frosty winter morning. The real appeal of cycling is that it is so enjoyable. It has none of the difficulties and tensions of other ways of traveling so you are more cheerful after a ride, even though the rush hour.

The first thing a non-cyclist says to you is: "But isn't it terribly dangerous?" It would be foolish to deny the danger of sharing the road with motor vehicles and it must be admitted that there are an alarming number of accidents involving cyclists. However, although police records indicate that the car driver is often to blame, the answer lies with the cyclist. It is possible to ride in such a way as to reduce risks to a minimum.

If you decide to join the thousands in Britain who are now returning to cycling as a cheap, satisfying form of transport your first problem will be trying to decide what bike to buy. Here are three simple rules for buying a bike:

1. Always buy the best you can afford. Of course there has to be a meeting point between what you would really like and economic reality, but aim as high as you can and you will get the benefit not only when you ride but also if you want to sell. Well-made bikes keep the value very well. And don't forget to include in your calculations the fact that you'll begin saving money on

fares and petrol the minute you leave the shop.

2. Get the best frame, the main structure of the bicycle, for your money as you can. Cheap brakes, wheels or gears can easily be replaced by more expensive ones, but the frame sets the upper limit on any transformation. You should allow for the possibility our cycling ambitions will grow with practice. When you begin, the four miles to work may the most you ever dream of, but after a few months a Sunday ride into the country begins to look more and more desirable. The best thing is to buy a bike just a little bit better than you think you'll need, and then grow into it. Otherwise, try to get a model that can be improved.

3.The fit is vital. Handlebars and seat height can be adjusted but you must get the right sized frame. On the whole it is best to get the largest size you can manage. Frame sizes are measured in inches and the usual adult range is from 21 inches to 25 inches, though extreme sizes outside those measurements can be found. Some people say if you take four inches off from your inside leg measurement you will end up with the right size of bike. The basic principle though is that you should be able to stand with legs either side of the crossbar (the bar that goes from the handlebars to the seat) with both feet comfortably flat on the ground.

Question 47: People who are buying their first bicycle are advised to __________.

A. buy a cheap model to begin with

B. get a bicycle which suits their current needs

C. buy as big a bicycle as they can afford

D. spend as much money on a bicycle as they can