单选题 When amphibians first appeared on Earth millions of years ago, the amount of ultraviolet radiation penetrating Earth's atmosphere was much greater than it is today. Therefore, current dramatic decreases in amphibian populations cannot be the result of recent increases in ultraviolet radiation penetrating Earth's atmosphere.
Which of the following is an assumption on which the argument depends?

A、 The eggs of modern amphibians are not significantly more vulnerable to ultraviolet radiation than the eggs of the first amphibians were.
B、 Modem amphibians are not as likely as the first amphibians were to live in habitats that shield them from ultraviolet radiation.
C、 Populations of modern amphibians are not able to adapt to changing levels of radiation as readily as populations of early amphibians were.
D、 The skin of amphibians is generally more sensitive to ultraviolet radiation than the skin of other animals is.
E、 (E) The skin of amphibians is less sensitive to ultraviolet radiation than to other types of radiation.

【正确答案】 A

【答案解析】[解析] 本题的推理为“因为早期紫外线辐射比现在强，所以现在两栖动物的剧减不能归因于紫外线辐射的增加”。(A)说明现在两栖动物的卵并不比最初两栖动物的卵更显著地易受伤害，显然是上述推理成立的必要条件，所以(A)正确。