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?
The numbers of the Baltimore oriole, a songbird that does not eat budworms but is as dependent on South American coffee plantations as is the Tennessee warbler, are declining.
The spruce budworm population has dropped because of a disease that can infect budworms but not Tennessee warblers.
The drop in the population of the spruce budworm is expected to be only temporary.
Many Tennessee warblers have begun migrating in the fall to places other than traditional coffee plantations.
Although many North American songbirds have declined in numbers, no other species has experienced as great a decline as has the Tennessee warbler.
P1:W减少了,Coffee(C)减少了
C1:W是因为C减少而减少
P2:Warbler(W)减少了,Bud(B)也减少了
C2:W的减少是因为B的减少
A选项,虽然没有直接提到W,但是举了一个和W一样的例子,证明了,在B不减少的情况下,W还是减少。
但是这道题同时又加强了第一个相关推理,表明,没有第三方因素(B)的导致W减少
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