Câu hỏi:
17/03/2020 252Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 43 to 50.
A useful definition of an air pollutant is a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetaions, 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 concentrations of these pollutants were 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 this localized regions, human output may be dominant and may temporarily overload the natural purification scheme of the cycle. 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 littleuntil we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfurdioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, as a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.
Question 49:
According to the passage, the numerical value of the concentration level of a substance is only useful if ___________.
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Trả lời:
Đáp án C
Dịch nghĩa: Theo như đoạn văn, sự tập trung cao độ của một chất chỉ có lợi khi ________.
A. các chất khác trong khu vực đều được biết đến
B. nó ở một vùng riêng biệt
C. tỉ lệ xuất hiện tự nhiên được biết đến
D. nó có thể được tính toán nhanh chóng
Giải thích: Thông tin ở đoạn cuối “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”
Đã bán 152
Đã bán 114
Đã bán 132
Đã bán 47
CÂU HỎI HOT CÙNG CHỦ ĐỀ
Câu 1:
Mark the letter A, B, C or D to indicate the underlined part that needs correction in each of the following questions.
Question 7: Until the invention of the telephone, skyscrapers were not consider very practical.
Câu 2:
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
Question 17: It would have been a much more serious accident ________ fast at the time.
Câu 3:
Mark the letter A, B, C or D to indicate the word or phrase that is OPPOSITE in meaning to the underlined part in each of the following questions.
Question 25: Some animals make identical sounds when they sense danger. Thus, they appear to be communicating with each other.
Câu 4:
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
Question 12: After the accident, the police informed the victim's next of __________.
Câu 5:
Mark the letter A, B, C or D to indicate the word/phrases SIMILAR in meaning to the underlined word(s) in each of the following questions.
Question 23: He is from such an unemotional family, he will never learn to unleash his feelings.
Câu 6:
Mark the letter A, B, C or D to indicate the sentence that best combines each pair of sentences in the following questions.
Question 30: She heard the news of the death of her mother. She fainted.
Câu 7:
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
Question 13: People living in areas need more help from charity organizations.
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