GWD 语法题一道。忘朋友们帮忙。

kobesoros

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.

A.    a greater proportion than it was
B.    ! a greater proportion than
C.    a greater proportion than they have been
D.    which is greater than was so
E.    which is greater than it has been

请告诉我 A 为什么错？

syflysun

please tell me what "it" in A refers to? That's why B is correct

kobesoros

Thanks for your help!