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

理解不了啊！！！

数量增加，感染机会减少

如果反复使用有可能被感染的食物的话，其感染机不会减少

所以如果只吃一次的话，那么随着其它数量增加，吃到被感染的食物的几率减少，从而感染机会减少

C

因为Ticks幼年期喂食infected white-footed mice而感染病菌，而Ticks幼年

期喂食的其他物种不会带菌，如果Ticks幼年期只喂一次的话，加上不带菌的喂食

物种数目增加，那食用不带菌物种的机会就大，那感染的机会就下降了。

不知道说明白了么！