[求助]GWD1-6回顾-8

Soaring television costs accounted for more than half the spending in the presidential campaign of 1992, a greater proportion than it was in any previous election.

1. a greater proportion than it was
2. a greater proportion than
3. a greater proportion than they have been
4. which is greater than was so
5. which is greater than it has been

为什么选c啊?其实我有点不明白的是这里比较的应该是proportion对吧，那是不是应该用单数呢? 总之就是很没有头绪

请指教~~

这道题题号是GWD-1-16。。。

以前有过比较充分的讨论的，CD的讨论更倾向于B

http://forum.chasedream.com/dispbbs.asp?boardid=23&replyid=517418&id=57841&page=1&skin=0&Star=1