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标题: PREP新-CR2-100 [打印本页]

作者: beckybear 时间: 2010-5-19 14:54 标题: PREP新-CR2-100

100. (30745-!-item-!-188;#058&005748) (T-9-Q28. ��ɽ-7-13 , different type)
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

答案怎么会选择B呢。
我的理解：
文章意思，风湿病是由于一种通过deer ticks传给人类的细菌引起的。一般来说，deer ticks带上这种病菌当它们还是幼虫的时候，通过吃infected white-footed mice. 然而，幼虫吃的一些其他的种类没有这个细菌。如果其他种类的老鼠增加了，更多的幼虫就会寄宿在没有感染的宿主上，所以感染这个细菌的ticks就会减少。
下面哪个应该要evaluate。
A。是否tick能寄宿的其他种类只有在white-footed mice也在的地方才能找到
B。时候tick的数量现在被限制了，因为tick幼虫可以寄宿的动物（不available）
C。明显不对。。
D。是否ticks在幼年时候没有被感染可以在成年时候被感染，当寄宿在infected deer曾经寄宿过的deer身上
E。无关选项。。
我怎么觉得应该是选择A呢。。

作者: starlight 时间: 2010-5-19 15:21

回复 1# beckybear

增加其他种类老鼠，虱子幼虫就能寄生在未感染的宿主身上，虱子感染就少，人类感染风湿就少

Ｂ：虱子的数量是否受限于幼虫对宿主的可利用性。如果虱子的数量不是由幼虫对宿主的可利用性决定的，那么题干的推理就不能成立了，因为题干一直在讨论在幼虫宿主上做文章，来降低感染虱子的数量，从而降低风湿病。
但是这里有一点，虱子的数量和受感染虱子的数量是不一样的。所以Ｂ还是有些瑕疵的,但GMAT需要选相对好的选项

Ａ：是否白腿老鼠和其他种类的宿主老鼠住在一样的地方。因为题干已经说了If the population of these other species were increased, more of the larvae would be feeding on uninfected hosts，因此这个逻辑部分已经被填充好了，不管这几个宿主是否住在一样的地方，只要其他的数量增加了，就会有更多的幼虫寄生在未感染的宿主上～
讲的不太清楚，还请多多指教～

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