[求助]GWD14 16又是比较，请各位XDJM看看。

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

答案是B，ＤＥ中which应该是指代不明，排除。C中costs(they)作比较了。但是A和B比的话不是更好吗？it 可以带half吧？