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.
I have done a search, but the explanation provided is not persuasive at all.
GWD-1-Q16
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 greater proportion than it was
a greater proportion than
a greater proportion than they have been
which is greater than was so
which is greater than it has been
OA is B. However, I think B is a incomplete sentence.
Two ways to complete it:
(1) "a greater propotion than they did", "they" refer to "television costs".
(2)"a greater proportion than it was", "it" refer to the proportion of spending on TV in the previous elections.