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.

For which of the following reasons can natural pollutants play an important role in controlling air pollution?

A. They function as part of a purification process.

B. They occur in greater quantities than other pollutants.

C. They are less harmful to living beings than other pollutants.

D. They have existed since the Earth developed.

Answer 1

Đáp án A.

Key words: natural pollutants, controlling air pollution, nature.

Câu hỏi: Dưới những lí do sau, đâu là lí do để chất gây ô nhiễm giữ vai trò quan trọng trong kiểm soát ô nhiễm không khỉ?

Clue: "Many of the more important air pollutants... are found in nature... 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": Nhiều trong số các chất ô nhiễm không khí... được tìm thấy trong tự nhiên... chúng trở thành thành phần trong chu trình sinh địa. Các chất này có vai trò như một kế hoạch thanh lọc không khí bằng cách cho phép hợp chất di chuyển từ không khí sang nước hoặc đất.

Phân tích: Từ Clue có thể tóm tắt lại là các chất gây ô nhiễm trong tự nhiên trở thành các chất hóa học khác, chất hóa học này lại tạo quy trình thanh lọc. Do vậy, các chất gây ô nhiễm trong tự nhiên là một phần của quá trình thanh lọc này. Chọn đáp án A. They function as part of a purification process.

Các đáp án khác:

  B. They occur in greater quantities than other pollutants: Các chất này hình thành với khối lượng lớn hơn các chất ô nhiễm khác - Không có thông tin.

  C. They are less harmful to living beings than other pollutants: Các chất này ít gây hại đến các sinh vật sống hơn các chất ô nhiễm khác - Không có thông tin.

   D. They have existed since the Earth developed: Chúng đã tồn tại kể từ khi Trái Đất hình thành - Không phải là một vai trò của ô nhiễm không khí.