时间状语比较问题

joseph_tx85

51.   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（A）

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

"than when..."可类似于"than before"，可以不补全，那 "than x years ago" （大全10， 22， &299），一样是时间状语不同的比较，为什么就必须补全"it was"呢?

joseph_tx85

up,nn快现身啊~

howardwang

为何不将题目全贴出来？这样便于讨论！

省略要根据不同的情况，最重要的一点是简洁但不能引起歧义。