GWD（TN）13-Q28

viviansecret

T-9-Q28.
            天山-7-13

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 from feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline.

Which of the following, if true, most strengthens the argument?

 

A.    Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans.

B.    There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice.

C.    A deer tick feeds only once while in the larval stage.

D.    A single host animal can be the source of bacterium for many tick larvae.

E.     None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans

答案：C。这道题非常不明白，请nn指教下！！！！：）

viviansecret

UP!

briandotnet

我的想法:

命题是:增加其他物种从而降低老鼠的比例,可以降低人得病的几率.

下面看选项

A 讲虱子不得病,成立与否与命题无关

B 讲没有人与老鼠接触的病的case, 如果成立,会削弱命题中关于老鼠和的病的关系

C 如果虱子只寄生(我不知道这个feed on在这里到底是吃还是寄生,anyway...)一次的话,加上命题中提到的增加其他物种,那么虱子的带菌率就会降低从而降低人的感染率.加强命题.

D 一只寄主可以吧细菌传给很多虱子,与命题无关.

E 讲除老鼠以外的寄主不携带任何可以被虱子传给人的病菌,这个跟lyme病毫无关系.

viviansecret

这道题我明白了，这里自己给自己重讲一遍：原文的核心在于，耗子把疾病传给骚扰过它的虱子，然后虱子又把病传给人类。如果虱子可以骚扰n多物种，而耗子只是n个物种之一，那简单化处理的话假设虱子骚扰耗子的概率是1/n，那如C选项所说，虱子总共只骚扰一次，那传病概率就可以近似估计为1/n，而C取反的话，假设虱子骚扰了3次，那么传病概率就是1-[(n-1)/n]^3，这个结果是要大于1/n的。所以C选项所说如果只骚扰一次，那n变大会对更显著的降低最后患病概率。个人理解，若是偶错了，欢迎拍砖！

[此贴子已经被作者于2009/8/12 6:54:58编辑过]