Air pollution is one of the most pervasive environmental problems because atmospheric currents can carry contaminated air to eve

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问题     Air pollution is one of the most pervasive environmental problems because
atmospheric currents can carry contaminated air to every part of the globe.
Most air pollution comes, from automobile emissions and from power plants
what burn coal and oil to produce energy for industrial and consumer use.          【S1】______
Carbon dioxide and other harmful gases releasing into the air from these           【S2】______
sources adversely effect weather patterns and the health of people, animals and    【S3】______
plants.
    Industrialized nations produce most of the world’s air pollution. For          【S4】______
example, because the United States is home to just 5 percent of the world’s
population, the country generates 22 percent of human-made carbon dioxide          【S5】______
emissions or 19 percent of all greenhouse gases such as carbon dioxide and         【S6】______
methane. These emissions harm the environment by leading acid rain and
global warming, and by depleting (使衰竭) the protective ozone layer which         【S7】______
surround the earth.
    Acid rain, a serious threat around the world, occurs when sulfur dioxide
and nitrogen oxide emissions from automobiles and fossil-fuel burning power        【S8】______
plants to fall back to Earth as acidic precipitation. Acid rain has contaminated
many lakes in Canada and the northeast United States and has been
documented even in the non-industrial state of Hawaii. In the United               【S9】______
Kingdom, 57 percent of all trees are severely defoliated (使落叶) owe to           【S10】______
corrosive fallout, and production of food crops has been declined in many parts
of the world. Acid rain has eroded the surfaces of great art and architectural
treasures, including the ancient sculptures of Rome and the Sphinx in Egypt.
【S8】

选项

答案plants to fail→plants fall

解析 从上下文看,本句讲酸雨的发生,从汽车和电厂排放出来的二氧化硫和氧化氮落到地面上时就会形成酸雨, when后面的时间状语从句中主语是sulfur dioxide and nitrogen oxide emissions,谓语是fall back to,因此fall前面不需要加to。
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