The role of governments in environmental management is difficult but inescapable. Sometimes, the state tries to manage the resou

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问题     The role of governments in environmental management is difficult but inescapable. Sometimes, the state tries to manage the resources it owns, and does so badly. Often,【C1】______. governments act in an even more harmful way. They actually subsidize the exploitation and【C2】______of natural resources. A whole【C3】______of policies, from farm-price support to protection for coal-mining, do environmental damage and(often) 【C4】______no economic sense. Scrapping them offers a two-fold【C5】______: a cleaner environment and a more efficient economy. Growth and environmentalism can actually go hand in hand, if politicians have the courage to【C6】______the vested interest that subsidies create.
    No activity affects more of the earth’s surface than farming. It shapes a third of the planet’s land area, not【C7】______Antarctica, and the proportion is rising. World food output per head has risen by 4 per cent between the 1970s and 1980s mainly as a result of increases in【C8】______from land already in【C9】______, but also because more land has been brought under the plough. Higher yields have been achieved by increased irrigation, better crop breeding, and a【C10】______in the use of pesticides and chemical fertilizers in the 1970s and 1980s.
    All these activities may have【C11】______environmental impacts. For example, land clearing for agriculture is the largest single【C12】______of deforestation; chemical fertilizers and pesticides may【C13】______water supplies; more intensive farming and the abandonment of fallow periods【C14】______exacerbate soil erosion; and the spread of monoculture and use of high-yielding varieties of crops have been accompanied by the【C15】______of old varieties of food plants which【C16】______some insurance against pests or diseases in future. Soil erosion threatens the productivity of land in both rich and poor countries. The United States,【C17】______the most careful measurements have been done, discovered in 1982 that about one-fifth of its farmland was losing topsoil at a rate【C18】______to diminish the soil’s productivity. The country subsequently【C19】______a program to convert 11 per cent of its cropped land to meadow or forest. Topsoil in India and China is【C20】______much faster than in America.
【C16】

选项 A、must have been provided
B、might have provided
C、must have provided
D、might have been provided

答案B

解析 本题测试语法。must have been provided表示一种肯定推测;might haveprovided表示一种可能的猜测;must have provided表示一种肯定推测;mighthave been provided表示一种可能的猜测。根据后面的some insurance againstpests or diseases in future可知,本句话表示一种可能性,并且应该用主动语态,所以应该选B。
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