[求助]OG11-72

72. The gyrfalcon，an Arctic bird of prey, has survived a close brush with extinction；its numbers are now five-times greater than when the use of DDT was sharply restricted in the early 1970’s．

(A)  extinction；its numbers are now five times greater than

(B)  extinction：its numbers are now five times more than

(C)  extinction，their numbers now fivefold what they were

(D)  extinction，now with fivefold the numbers they had

(E)  extinction，now with numbers five times greater than

答案：A

我对答案没有异议。一个问题是：为什么这里用its numbers而不是its number?

有NN给解释一下？

哦，they不对~