GWD13_28 (TN版)

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

正确答案为： C

这是怎么推导的啊？

比如1个虱卵，以前有10个带菌老鼠，10个无菌老鼠，那么每一次进食传上的概率是50%（情况一）

仍是一个虱子卵，仍是有10个带菌老鼠，40个无菌老鼠的话，那么每一次进食传上的概率是25%（情况二)

C加强，因为限定了只叮咬一次，那么必然得到降低传染率的结论。但是如果不限定的话，那么可能有的卵吃一次，有的卵是三次，那么比如情况一下叮两次，就等于情况二下叮一次的概率；情况一下叮三次就小于情况二下叮一次的概率，所以C规避的其他可能，因此起到加强作用。