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标题: prep08 第100题求解 [打印本页]

作者: cocoers 时间: 2015-5-19 12:32
标题: prep08 第100题求解
100. (31888-!-item-!-188;#058&006228) (GWD 3-Q17)

Brochure: Help conserve our city’s water supply. By converting the landscaping in your yard to a water-conserving landscape, you can greatly reduce your outdoor water use. A water-conserving landscape is natural and attractive, and it also saves you money.
Criticism: For most people with yards, the savings from converting to a water-conserving landscape cannot justify the expense of new landscaping, since typically the conversion would save less than twenty dollars on a homeowner’s yearly water bills.
Which of the following, if true, provides the best basis for a rebuttal of the criticism?
A. Even homeowners whose yards do not have water-conserving landscapes can conserve water by installing water-saving devices in their homes.
B. A conventional landscape generally requires a much greater expenditure on fertilizer and herbicide than does a water-conserving landscape.
C. A significant proportion of the residents of the city live in buildings that do not have yards.
D. It costs no more to put in water-conserving landscaping than it does to put in conventional landscaping.
E. Some homeowners use more water to maintain their yards than they use for all other purposes combined.
这道题答案是B，但是D为什么错？如果成年时也会感染的话，那么感染病菌的ticks不是并没有减少吗？

作者: cocoers 时间: 2015-5-19 12:42
发错了。。。。。应该是这道
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

作者: alzn2765 时间: 2015-5-21 14:11

cocoers 发表于 2015-5-19 12:42
发错了。。。。。应该是这道
100. (30745-!-item-!-188;#058&005748) (T-9-Q28. ��ɽ-7-13 , different t ...

这道题的基本逻辑就是放一种没病的老鼠让跳蚤吃，如果大部分跳蚤吃的都是没病的老鼠，那么长大了也是没病的跳蚤就会比较多，把病菌传染给人的概率就低了。

这道题的“隐藏”逻辑就是默认答题者知道跳蚤的幼虫一定是跳蚤生的。

B的意思是现在跳蚤的数量是不是受到食物太少的限制。如果是，食物多了跳蚤就多了，那么把卵产在有病的老鼠的尸体上的跳蚤就多了，以后带病的跳蚤number不会减少，反而增加。如果不是，就是跳蚤就那么“固定数量”的几只，把感染的老鼠的百分比降低，自然跳蚤吃到有病老鼠的概率降低了，长大后感染的跳蚤的number就变少了。

D的意思是搞清楚这个病菌会不会通过血液在成年跳蚤之间传染，把本来没感染的跳蚤变成有病的跳蚤。这个搞清楚了只能明确感染的跳蚤在跳蚤的百分比会上升，但不代表其绝对的number一定增加或者减少（有可能总体数量变少了，即使百分比增加，绝对的数量反而减少），这样就没有办法评估方案了。

这道题考的核心还是百分比与绝对数量的概念的掌握。

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