Amphibian populations are declining in numbers worldwide. Not coincidentally, the earth's ozone layer has been continuously depleted throughout the last 50 years. Atmoshpere ozone blocks UV-B, a type of ultraviolet radiation that is continuously produced by the sun, and which can damage genes. Because amphibian lack hair, hide, or feathers to shield them,they are particularly vulnerable to UV-B radiation. In addition, their gelatinous eggs lack the protection of leathery or hard shells. Thus, the primary cause of the declining amphibian population is the depletion of the ozone layer.
Each of the following, if true, would strengthen the argument EXCEPT:
A, Of the various type of radiation blocked by atmospheric ozone, UV-B is the only type that can damage genes.
B, Amphibian population are declining far more rapidly than are the population of nonamphibian species whose tissues and eggs have more natural protection from UV-B.
C,Atmospheric ozone has benn significantly depleted above all the areas of the world in which amphibian populaitons are declining.
D, The natural habitat of amphibians has not become smaller over the past century.
E,Amphibian populations have declined continuously for the last 50 years.
答案是A， 我觉得A应该是加强作用了吧？臭氧层变薄导致UV-B对amphibian危害更大导致amphibian人口下降。 D 是无关选项吗？怎样区分不加强和无关选项？ 请大家赐教。感谢！
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发表于 2009-12-8 00:14:48
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