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. 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
Can someone tell me why the answer is "C" instead of "B" ? What is "they" referring to ??? thanks.