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  3. Desertification in the arid United Statse is flagrant. Groundwater supplies beneath vast stretches of land are dropping precipit

Desertification in the arid United Statse is flagrant. Groundwater supplies beneath vast stretches of land are dropping precipit

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问题     Desertification in the arid United Statse is flagrant. Groundwater supplies beneath vast stretches of land are dropping precipitously. Whole river systems have dried up. Others are chocked with sediment washed from denuded land. 21. Hundreds of thousands of acres of previously irrigated cropland have been abandoned to wind or weeds. Several million acres of natural grassland are eroding at unnaturally high rates as a result of cultivation or overgrazing. All told, about 225 million acres of land are undergoing severe desertification.
    22. Federal subsidies encourage the exploitation of arid land resources. Low-interest loans for irrigation and other water delivery systems encourage farmers, industry, and municipalities to mine groundwater. Federal disaster relief and commodity programs encourage arid-land farmers to plow up natural grassland to plant crops such as wheat and, especially cotton. Federal grazing fees that are well below the free market price encourage overgrazing of the commons. The market, too, provides powerful incentives to exploit arid land resources beyond their carrying capacity. 23. When commodity prices are high relative to the farmer’s or rancher’s operating costs, the return on a production-enhancing investment is invaribly greater than the return on a conservation investment. And when commodity prices are relatively low, arid land ranchers and farmers often have to use all their available financial resources to stay solvent.
    24. If the United States is, as it appears, well on its way toward overdrawing the arid land resources, then the policy choice is simply to pay now for the appropriate remedies or pay far more later, when productive benefits from arid land resources have been both realized and largely terminated.
选项
答案如果商品价格高于农场主或牧场主的经营成本，那么旨在增加产出的投资的回报永远大于自然资源管理投资的回报。如果商品价格比较低，干旱地区的牧场主和农场主则往往必须耗尽所有的财力，以免负债。
解析
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