GWD TN 2-38 或 GWD3-Q38

herway

GWD3-Q38:

Kate:  The recent decline in numbers of the Tennessee warbler, a North American songbird that migrates each fall to coffee plantations in South America, is due to the elimination of the dense tree cover that formerly was a feature of most South American coffee plantations.

Scott:  The population of the spruce budworm, the warbler’s favorite prey in North America, has been dropping.  This is a more likely explanation of the warbler’s decline.

Which of the following, if true, most seriously calls Scott’s hypothesis into question?

A.    The numbers of the Baltimore oriole, a songbird that dose not eat budworms but is as dependent on South American coffee plantations as is the Tennessee warbler, are declining.

B.    The spruce-budworm population has dropped because of a disease that can infect budworms but not Tennessee warblers.

C.    The drop in the population of the spruce budworm is expected to be only temporary.

D.    Many Tennessee warbler have begun migrating in the fall to places other than traditional coffee plantations.

E.     Although many North American songbirds have declined in numbers, no other species has experienced as great a decline as has the Tennessee warbler.

A项，Baltimore oriole数量减少也可能因为其它原因，如人类捕杀等，不能说明Scott是错的。

D项为什么是无关呢？

D项，many Tennessee warbler迁徙到非traditional coffee plantation的地方，是致使Tennessee warbler迁徙到South American coffee plantations的数量下降的原因，因此削弱了Scott的假设。

仔细想想虽然D项可能也不够说服力，但我认为比起A来好一点。

盼帮助，谢谢～

alohabrian

不能把A的削弱理解成这样: Baltimore birds不是因为budworm少了，而数量少的。所以warblier的数量少，也不是因为budworm的数量delcine了。            这种类比法削弱是没道理的。

而
要这样理解：Baltimore同样也飞去coffee
plantation,在不受budworm数量减少影响的情况下，Baltimore的数量也少了，证明有可能有其他原因比如
树少了，使得baltimore数量少了。 那么 warbler也依赖 coffee plantion,也有可能是因为
树少了（他因在这里），数量下降的。

D，说这些鸟飞到迁到其他地方去，不能解释，它们为什么总体数量变少。注意看原文，并不是说这些鸟的数量只在南美的coffee plantation减少。

      所以D不能成为 鸟儿 数量减少的 他因。

[此贴子已经被作者于2009-3-19 0:25:44编辑过]