Question

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.

It can be inferred from the first paragraph that __________.

A. water vapor is an air pollutant in localized areas

B. most air pollutants today can be seen or smelled

C. the definition of air pollution will continue to change

D. a substance becomes an air pollutant only in cities

Answer 1

Đáp án C.

Key words: inferred, first paragraph.

Câu hỏi: Có thể suy ra điều gì từ đoạn đầu tiên?

Clue: "Air pollution requires a very flexible definition that permits continuous change": Ô nhiễm không khí đòi hỏi một định nghĩa linh hoạt cho phép sự thay đổi liên tục.

Phân tích: Dựa vào Clue ta thấy định nghĩa về ô nhiễm không khí do đó sẽ còn thay đổi. Chọn đáp án: C. the definition of air pollution will continue to change.

Các đáp án khác không phù hợp:

  A. water vapor is an air pollutant in localized areas: hơi nước là ô nhiêm không khí ở các khu vực chuyên môn hóa.

  B. most air pollutants today can be seen or smelled: hầu hết ô nhiễm không khí ngày nay có thế nhìn được hoặc ngửi được.

  C. a substance becomes an air pollutant only in cities: một chất trở thành ô nhiễm không khí chỉ khi ở thành phố.