This was my thought process as I approached the problem:

In solution A, the singular pronoun "it" is wrong because the dependent clause should be referring to "costs," a plural antecedent.

D and E are wrong because the relative pronoun "which" introduces a non restrictive clause and needs to refer to the noun directly preceding it. In this case it modifies "1992," which doesn't make sense. "Which" needs to logically modify "costs."


Between B and C, "a greater proportion" by itself is ambiguous. Is it a greater proportion of costs? spending? campaign? This can refer to any of the preceding nouns, so we really need a pronoun to resolve the ambiguity. C is correct because it uses the pronoun "they."


To answer your other question, perfect tenses are used to indicate a time relationship between events. Present perfect is used because costs were greater in the past and continue until the present. We don't use simple past tense here because the phenomenon of increasing costs can continue in the present and maybe even into the future.

HTH!

GMATBootcamp wrote:This can refer to any of the preceding nouns, so we really need a pronoun to resolve the ambiguity. C is correct because it uses the pronoun "they."

So who is they referring to? Since the preceding clause does not have a subject, they does not have a clear antecedent.

I opted B too for the same reason.

IMO C.

The only three nouns in the preceding dependent clause are costs, spending, and campaign.

This means that the plural pronoun they can only refer to the noun costs


HTH!

GMATBootcamp wrote: To answer your other question, perfect tenses are used to indicate a time relationship between events. Present perfect is used because costs were greater in the past and continue until the present. We don't use simple past tense here because the phenomenon of increasing costs can continue in the present and maybe even into the future.
HTH!

Thanks Paul. I had another question regarding Present Perfect usage in this sentence. This sentence talks about soaring television costs in elections, which may or may not happen in the present or the future. It is only one time expenditure that happened in 1992. So, I was wondering if the context warrants Present Perfect?

If there was an option such as:
"a greater proportion than they were"
would you still choose C over this?

this question is from 15 testset. OA is C. but OA have a problem

"have been..." can not go with "in any previous election"

a past tense must go with time adverb which show clearly of past.

"cost were..." is quite in the past. the increasing is not relative here and we can not use present perfect