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?
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AThe 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.
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BThe spruce-budworm population has dropped because of a disease that can infect budworms but not Tennessee warblers.
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CThe drop in the population of the spruce budworm is expected to be only temporary.
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DMany Tennessee warbler have begun migrating in the fall to places other than traditional coffee plantations.
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EAlthough many North American songbirds have declined in numbers, no other species has experienced as great a decline as has the Tennessee warbler.
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正确答案: A