prep08-cr2-100 求解！

Knightll

Lyme disease is caused by a bacterium transmitted to humans by deer ticks.  Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice.  However, certain other species on which the larvae feed do not harbor the bacterium.  If the population of these other species were increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.
Which of the following would it be most important to ascertain in evaluating the argument?  

A. Whether populations of the other species on which deer tick larvae feed are found only in areas also inhabited by white-footed mice
B. Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on
C. Whether the infected deer tick population could be controlled by increasing the number of animals that prey on white-footed mice
D. Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed
E. Whether the other species on which deer tick larvae feed harbor any other bacteria that ticks transmit to humans

为什么答案是B呢? D错在哪？

songxueb

本文的结论是：如果其他deer tick幼虫寄主动物数量能够增加，那么更多的

幼虫将会寄食在没有感染的寄主身上，因此感染这一细菌的tick数量将会减少。
这个结论有个明显的问题，就是绝对数和相对比例的问题，如果其他deer tick幼

虫寄主动物数量能够增加，那么更多的幼虫将会寄食在没有感染的寄主身上，在

感染这一细菌的tick数量基本不变的前提下，感染这一细菌的tick的比例，占所

有tick的比例将可能会减少。而本文的结论是：因此感染这一细菌的tick数量将

会减少。应该说，没有感染这一细菌的tick数量增加与否，与本文的结论--感染

这一细菌的tick数量将会减少，并没有这接关系，这个两者之间只是相对比例，

或者各自占整体的比例有关系，绝对数量，彼此并没有关系。
因此，要得出本文的这一结论--感染这一细菌的tick数量将会减少，影响这一结

论的重要因素就是答案B. 其实答案B还可以整出很多变形，但是万变不离其中，

核心就是要说：感染这一细菌的tick数量是否会变化。

Knightll

谢谢! 看你的解释我B 是想通了，但现在我又不知道C错在哪了。
我对C的理解是：如果是 can be controled, 那么 the infected deer tick population 就会减少，加强结论。如果can not be controled, 那么就不会影响到受感染的tick 数量，不能确定tick的数量是增多还是变少，不就是削弱结论了吗？这个选项不是单纯地在讲绝对数量吗？之所以选B 是不是因为它的加强和削弱结论的力度最大？

Knightll

嗯，我明白了。再次感谢啊！