蓝皮SC70，主系表结构比较在时态不一致时是否必须补出助动词？

reuentalv

在Prep笔记中，对于主系表结构的比较，总结为如果时态不一致，必须补出助词，举例如下：The economy of Florida is more diversified than it was ten years ago.

但是OG蓝皮Verbal第70题如下：

70. 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

答案选A。我想问这句话补充完整的话是不是：Its numbers are now five times greater than (its numbers were) when the use of DDT was sharply restricted in the early 1970’s. 表示gyrfalcon的数量在1970年和现在的变化。如果是这样的话，时态就不一致了，为什么还可以省略呢？

lala974

同问！

aeoluseros

如果完全不会造成句子的含糊，主谓可以同省，如70题than后面跟着when，when引导的一定是状语。
而例句more diversified than it was ten years ago.
ten years是名词，紧随than不好，好像是ten years与economy的比较，外表上不完美，所以加上it was。