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 43 to 50.
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 changes. 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 more important air pollutants, such as sulfur oxides, carbon monoxides 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 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. the definition of air pollution will continue to change.
B. Most air pollutants today can be seen or smelled.
C. a substance becomes an air pollutant only in cities.
D. water vapor is an air pollutant in localized areas.
Kiến thức: Đọc hiểu
Giải thích:
Có thể suy ra từ đoạn văn thứ nhất rằng _______.
A. định nghĩa về ô nhiễm không khí sẽ tiếp tục thay đổi.
B. Hầu hết các chất gây ô nhiễm không khí ngày nay có thể được nhìn thấy hoặc ngửi thấy mùi.
C. một chất trở thành một chất gây ô nhiễm không khí chỉ ở các thành phố.
D. hơi nước là một chất ô nhiễm không khí trong khu vực địa phương hóa.
Dẫn chứng: Air pollution requires a very flexible definition that permits continuous changes.
Tạm dịch: Ô nhiễm không khí đòi hỏi một định nghĩa rất linh hoạt cho phép thay đổi liên tục.
Đáp án: A