求教gwd 1-16

qiuqiaomm

Q16: 原答案C现选B

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c不对啦？