时间状语比较问题

sportman

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?

steveyangxt

另外补不补也是有据可依的。看人家不用补的时间前面都有介词，可以不补。你孤零零的一个时间，就必须补，不补造成对比对象不同了。

sammen

补全的问题是这样的,ETS要求都要补全的,但是这里补出的选项都有明显的错误是correct性质的错误,所以只能选没有补出的.我的建议是以后都尽量补出,实在是补出的选项错的很厉害,就选省略的.