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 does 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 warblers 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. 答案是A 能理解A 是答案，但是不明白B,C是怎么排除的，NN们帮忙解答下吧~~~~~~~~ B说spruce budworm的减少不会影响TW，貌似可以削弱啊。。。？? 还有C 也晕呼呼的。。作者: 孤独的长跑者 时间: 2010-9-5 10:12
虫少了＝〉鸟没得吃了＝〉鸟少了。 Ｂ／Ｃ都没断这个桥。鸟不是染了虫子的病而死，而是没有吃的了。临时还是长期不是题目讨论的问题。作者: cartier921 时间: 2010-9-5 10:20
能不能再 说得详细点，没看懂作者: cartier921 时间: 2010-9-5 10:31
B 好像懂了， 蟲得病會減少，但是此病對鳥沒有影響，这与是不是虫子数量下降而引起的鸟数量下降无关 但是C 说虫子的减少是暂时的，但是鸟的数量还是在下降，说明不是虫子数量下降影响鸟数量下降的？作者: tianlingfrl 时间: 2010-9-5 10:52
C可以是一个加强第二种观点的选项~也就是说，鸟的数量是由虫子数量决定的，由于虫子数量是短时间下降，于是可以预见，虫子数量增加时，鸟的数量也会增加~削弱了第一种观点中，鸟的数量是由树木决定的观点~不过也可以说是个无关项，因为没有提到任何关于未来情况发展的方向，只是单纯说了虫子数量下降的趋势~作者: cartier921 时间: 2010-9-5 11:14
