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 following questions.

American humor and American popular heroes were born together. The first popular heroes of the new nation were comic heroes, and the first popular humor of the new nation was the antics of its hero-clowns.

The heroic and the comic were combined in novel American proportions in popular literature. The heroic themes are obvious enough and not much different from those in the legends of other times and places: Achilles, Beowulf, Siegfried, Roland, and King Arthur. The American Davy Crockett legends repeat the familiar pattern of the old world heroic story: the pre-eminence of a mighty hero whose fame in myth has a tenuous basis in fact; the remarkable birth and precocious strength of the hero; single combats in which he distinguished himself against antagonists, both man and beast; vows and boasts; pride of the hero in his weapons, his dog, and his woman.

Davy Crockett conquered man and beast with a swaggering nonchalance. He overcame animals by force of body and will. He killed four wolves at the age of six. He hugged a bear to death; he killed a rattlesnake with his teeth. He mastered the forces of nature. Crockett’s most famous natural exploit was saving the earth on the coldest day in history. First, he climbed a mountain to determine the trouble. Then he rescued all creation by squeezing bear-grease on the earth’s frozen axis and over the sun’s icy face. He whistled, “Push along, keep moving!” The earth gave a grunt and began moving.

Neither the fearlessness nor the bold huntsman’s prowess was peculiarly American. Far more distinctive was the comic quality, all heroes are heroic; few are also clowns. What made the American popular hero heroic also made him comic. “May be”, said Crockett, “you’ll laugh at me and not at my book”. The ambiguity of American life and the vagueness which laid the continent open to adventure, which made the land a rich storehouse of the unexpected, which kept vocabulary ungoverned and the language fluid----this same ambiguity suffused both the Crockett legends were never quite certain whether to laugh or to applaud, or whether what they saw and heard was wonderful, awful or ridiculous.

What is the main point the author makes in the passage?

A. Davy Crockett wrote humorous stories about mastering the nature.

B. American popular heroes were characteristically comic.

C. The Davy Crockett stories reflected the adventurous spirit of early America.

D. American popular literature was based on the legends of other times and places.

Cho các cặp chất sau tác dụng với nhau ở điều kiện nhiệt độ thích hợp:

1) Mg + CO₂              2) Cu + HNO₃ đặc      3) NH₃ + O₂

4) Cl₂ + NH₃              5) Ag + O₃                 6) H₂S + Cl₂

7) HI + Fe₃O₄             8) CO + FeO

Có bao nhiêu phản ứng tạo đơn chất là phi kim?

A. 6

B. 5

C. 4

D. 7

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.

            An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled - a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

          Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities.

          However, human production usually occurs in a localized area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, has a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

According to the passage, human-generated air pollution in localized regions _______.       

A. will damage areas outside of the localized regions

B. will react harmfully with natural pollutants

C. can overwhelm the natural system that removes pollutants

D. can be dwarfed by nature's output of pollutants

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 following questions.

Although they are an inexpensive supplier of vitamins, minerals, and high-quality protein, eggs also contain a high level of blood cholesterol, one of the major causes of heart diseases. One egg yolk, in fact, contains a little more than two-thirds of the suggested daily cholesterol limit. This knowledge has driven egg sales to plummet in recent years, which in turn has brought about the development of several alternatives to eating regular eggs. One alternative is to eat substitute eggs. These egg substitutes are not really eggs, but they look somewhat like eggs when they are cooked. They have the advantage of having low cholesterol rates, and they can be scrambled or used in baking. One disadvantage, however, is that they are not good for frying, poaching, or boiling. A second alternative to regular eggs is a new type of egg, sometimes called 'designer' eggs. These eggs are produced by hens that are fed low-flat diets consisting of ingredients such as canola oil, flax, and rice bran. In spite of their diet, however, these hens produce eggs that contain the same amount of cholesterol as regular eggs. Yet, the producers of these eggs claim that eating their eggs will not raise the blood cholesterol in humans.

         Egg producers claim that their product has been portrayed unfairly. They cite scientific studies to back up their claim. And, in fact, studies on the relationship between eggs and human cholesterol levels have brought mixed result. It may be that it is not the type of eggs that is the main determinant of cholesterol but the person who is eating the eggs. Some people may be more sensitive to cholesterol derived from food than other people. In fact, there is evidence that certain dietary fats stimulate the body's production of blood cholesterol. Consequently, while it still makes sense to limit one's intake of eggs, even designer eggs, it seems that doing this without regulating dietary fat will probably not help reduce the blood cholesterol level.

The word 'portrayed' could best be replaced by which of the following?

A. studied  

B. destroyed          

C. tested      

D. described