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 30 to 34.
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.
The word “These” in the second paragraph is closest in meaning to _______.
A. The various chemical reactions
B.The pollutants from the developing Earth
C.The compounds moved to the water or soil 6
D. The components in biogeochemical cycles
Giải bởi Vietjack
Chọn D.
Đáp án D.
Giải thích:
Từ "these" trong đoạn thứ hai là gần nhất trong ý nghĩa với__________:
A. Các phản ứng hóa học khác nhau
B. Các chất gây ô nhiễm từ trái đất đang phát triển
C. Các hợp chất chuyển đến nước hoặc đất
D. Các thành phần trong chu kỳ sinh địa hóa
Ý trong bài : “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.”
(Khi Trái đất phát triển, sự tập trung vào các nhân tố gây ô nhiễm này bị thay đổi bởi các phản ứng hoá học, chúng trở thành những phần tử nằm trong chy kỳ hoá sinh. Những phần tử này hoạt động như 1 chu trình làm sạch không khí bằng cách cho phép các hợp chất này di chuyển từ không khí sang nước hay đất.)
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