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 ---- it does not have an antecedent..television costs is plural.
b) a greater proportion than -- correct
c) a greater proportion than they have been ---- have been signifies some event in the past which continues till present . So in this context the television costs is not something which is high till present day.
d) which is greater than so ---which signifies campaign of 1992
e) which is greater than it has been ---- which signifies campaign of 1992


















