请教：分号前后的代词指代问题

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146.   (32521-!-item-!-188;#058&007141)

 

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，以前看一些题说分号前后是两个独立的句子，所以代词不可以互相指代，如果是这样的话那这题里的its numbers的its指代谁呢？

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