prep 96题答案不理解。。。

gmatziyu

In some species of cricket, the number of chirps per minute used by the male for attracting females rise and fall in accordance with the surrounding temperature, and they can in fact serve as an approximate thermometer.

(A) for attracting females rise and fall in accordance with the surrounding temperature, and they can in fact serve

(B) for attracting females rises and falls in accordance with the surrounding temperature, which can in fact serve

(C) in attracting females rise and fall in accordance with the surrounding temperature, in fact possibly serving

(D) to attract females rises and falls in accordance with the surrounding temperature, and it can in fact serve

(E) to attract females rises and falls in accordance with the surrounding temperature, in fact possibly serving
答案D..我选e，虽然觉得possibly用法怪怪的。。
但是d中的it是指代什么呢？记得it 不可以指代前面一句话阿，这里的意思应该是指代`number rises and falls in accordance with....`
难道是指number么？。。。请教中....

果汁软糖

it指代number
这是并列的两句话，用and连接了两个完整的句子，表明了 the number of chirps per minute used by the male to attract females 变化的原因和其作用，后面的那句和前面的并不是从属关系。