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  3. The world has heard much about how the burning of fossil fuels causes the greenhouse effect, but little about how the burning of

The world has heard much about how the burning of fossil fuels causes the greenhouse effect, but little about how the burning of

admin2015-01-30  65
问题     The world has heard much about how the burning of fossil fuels causes the greenhouse effect, but little about how the burning of tropical rain forests also contributes to the greenhouse effect. And still less do we hear about how reforestation of these tropics could help heal an ailing world.
    The earth constantly maintains 700 billion metric tons of carbon dioxide(CO2)in the atmosphere. Fossil fuels emit another 5.2 billion metric tons of CO2 into the air each year, while the burning of tropical forests emits roughly 1.8 billion metric tons of CO2—both contributing to a buildup of carbon dioxide, although only about half accumulates in the skies while the rest disappears into oceans and lakes, vegetation and soil.
    【F1】Replanting trees in the tropics could eventually offer a solution to the greenhouse effect. One acre of a tropical plantation can absorb an annual average of four metric tons of atmospheric carbon. In order to soak up 1 billion metric tons of CO2 we would have to plant 400,000 square miles of new tropical forests. Plant enough trees and we could remove much of the additional CO2 building up in the atmosphere. Nowhere in the world are conditions better for growing trees than in the tropics, where year-round warmth and moisture encourage rapid growth. To start a grand-scale tree-growing project in the tropics, however, would require as many as 20 governments in Latin America, Africa, and Asia to stop the rapid destruction of rain forests.
    Reforesting the earth is not the definitive solution to the warming trend of the greenhouse effect. It is only one way to bring the rising levels of carbon in the atmosphere under control.【F2】A worldwide campaign to reforest the earth, however, will improve the quality of our lives, stabilize rising temperature, and buy time until we find additional solutions to the greenhouse effect.
The buildup of carbon dioxide in the atmosphere each year is______.
选项 A、7 billion metric tons
B、5.2 billion metric tons
C、1.8 billion metric tons
D、3.5 billion metric tons
答案D
解析
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本试题收录于： C类竞赛（非英语专业本科）题库大学生英语竞赛（NECCS）分类
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C类竞赛（非英语专业本科）

大学生英语竞赛（NECCS）

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