Prep语法题一道

coffeeqoo

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
答案是D，但想问一下D中and后的代词it指代什么？

wangmy820

应该指代的是the number of chirps per minute