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
According to the passage, human-generated air pollution in localized regions ________.
A. can be dwarfed by nature's output of pollutants
B. can overwhelm the natural system that removes pollutants
C. will damage areas outside of the localized regions
D. will react harmfully with natural pollutants
Đáp án B
Đề: Theo bài luận, ô nhiễm không khí gây ra bởi con người ở các khu vực tập trung dân cư…
A. có thể được lấn át bởi các chất gây ô nhiễm sinh ra từ tự nhiên.
B. có thể áp đảo hệ thống tự nhiên mà (hệ thống đó) loại bỏ các chất gây ô nhiễm.
C. sẽ gây thiệt hại tới các khu vực ngoài các vùng tập trung dân cư.
D. sẽ phản ứng một cách có hại với các chất gây ô nhiễm tự nhiên.
Đầu đoạn 3: “In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles.”
Dịch: Ở những vùng như vậy, khí thải do con người có thể chi phối và có thể tạm thời gây quá tải lên sự thanh lọc tự nhiên của các chu kỳ.