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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?

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

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

3. A deer tick feeds only once while in the larval stage.
4. A single host animal can be the source of bacterium for many tick larvae.

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

Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white-footed mice.

题干强调说只有在larval stage才可能吃mice感染

现在为了降低感染的可能性 我们增加别的species的数量 即让每feed一次感染的几率降低

试想 在这个特定的stage feed一次和feed多次感染的概率一样吗

显然不一样

如果只feed一次 那么就把这个计划成功的概率提到最高