关于assumption和strengthen？

38. Amphibianpopulations are declining in numbers worldwide. Not coincidentally, the earth’sozone layer has been continuously depleted throughout the last 50 years.Atmospheric ozone blocks UV-B, a type of ultraviolet radiation that iscontinuously produced by the sun, and which can damage genes. Becauseamphibians lack hair, hide, or feathers to shield them, they are particularlyvulnerable to UV-B radiation. In addition, their gelatinous eggs lack theprotection of leathery or hard shells. Thus, the primary cause of the decliningamphibian population is the depletion of the ozone layer.

Each of thefollowing, if true, would strengthen the argument EXCEPT:

A.     Of the various types ofradiation blocked by atmospheric ozone, UV-B is the only type that can damagegenes.

B.     Amphibian populations aredeclining far more rapidly than are the populations of non-amphibian specieswhose tissues and eggs have more natural protection from UV-B.

C.     Atmospheric ozone has beensignificantly depleted above all the areas of the world in which amphibianpopulations are declining.

D.     The natural habitat ofamphibians has not become smaller over the past century.

E.     Amphibian populations havedeclined continuously for the last 50 years.

选D。

答案说，D是中性评价，既不strengthen，也不weaken。

但是我认为，D相当于是排除了“amphibian变少”的独立第三方因素，从而对结论“臭氧减少导致amphibian变少”构成了支持。

这么一来，D就不该被except。

不知诸大神怎么看？