Câu hỏi:
13/08/2021 482Read 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 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 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 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.
The word “These” in the second paragraph is closest in meaning to __________.
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30 đề thi THPT Quốc gia môn Tiếng anh năm 2022 có lời giải !!
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Trả lời:
Giải bởi Vietjack
Đáp án B
Nhà sách VIETJACK:
CÂU HỎI HOT CÙNG CHỦ ĐỀ
Câu 1:
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
The biggest fear is that humans might _________ control over robots.
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12/08/2021
66,530
Câu 2:
Mark the letter A, B, C, or D on your answer sheet to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following questions.
He’ll give Joe a red rose and a lovey- dovey poem he wrote.
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13/08/2021
31,297
Câu 3:
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
The talks were meant to break down _________ between the two groups.
Xem đáp án »
12/08/2021
22,012
Câu 4:
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
I saw a terrible accident while I _________ on the beach.
Xem đáp án »
12/08/2021
20,652
Câu 5:
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
The Japanese market _________ 35 per cent of the company's revenue.
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12/08/2021
17,639
Câu 6:
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
I really enjoy being with my father. He has got a really good _________ of humour.
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13/08/2021
16,995
Câu 7:
Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.
They had sold out all the tickets _________.
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12/08/2021
15,202
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