[求助斑竹]OG-VR-SC-70关于than比较的用法

huangyouhuifei

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

正确答案：A
已经搜到以前的帖子但是，仍然有一个问题：
A是不是：“its numbers are now five times greater than （they were） when the use of ...”的省略？如果不是，为什么？如果是，为什么在前后时态不一样（are vs. were）的情况下，不把they were补全？

我记得在than比较前后的时态不一致的时候是应该把动词补出来的，只有时态一致的情况下才能省略。

问：下面三个句子的正确性？我觉得下面三个句子跟本题是一样的。
X has more money now than when the stock market crashed
X has more money now than in 1988
X has more money than he had in 1988

huangyouhuifei

叮叮叮：）

小鬼和灵

帮顶一下~我也想知道

Gail小M

http://forum.chasedream.com/GMAT_SC/thread-537203-1-1.html