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 from 22 to 28.
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
Which of the following is best supported by the passage?
A. To effectively control pollution, local government should regularly review their air pollution laws.
B. One of the most important steps in preserving natural lands is to better enforce air pollution laws
C. Scientists should be consulted in order to establish uniform limits for all air pollutants
D. Human activities have been effective in reducing air pollution
Đáp án D
Đề: Ý nào sau đây được bổ trợ tốt nhất bởi bài luận?
A. Để kiểm soát ô nhiễm một cách hiệu quả, chính phủ địa phương cần thường xuyên xem xét lại các luật về ô nhiễm môi trường của họ.
B. Một trong các bước quan trọng nhất trong việc bảo tồn đất đai tự nhiên là thi hành tốt hơn các luật về ô nhiễm môi trường.
C. Các nhà khoa học nên được hỏi ý kiến để thiết lập những giới hạn đồng bộ cho mọi chất gây ô nhiễm không khí.
D. Các hoạt động của con người đã và đang có hiệu quả trong việc giảm thiểu ô nhiễm không khí.