Explanation

The words filling the blank must be consistent with the idea that the ruling party needs to “shore up” its standing with the electorate. In their own way, Choices A, C, D, and F are consistent with that idea, but only two of these when taken together — “restive” and “skittish” — produce sentences that are alike in meaning.

“Aloof” fits the blank reasonably well, but there is no other word offered that is nearly alike in meaning. The same holds for “vociferous.” “Placid” and “tranquil” are similar in meaning but do not fit the context of the sentence.

Thus the correct answer is restive (Choice C) and skittish (Choice D).
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Read the sentence and look for contextual information.

The ruling party needs to build support from the _________ voters.
Unfortunately, there there isn't much contextual information provided to be certain of the "flavor" of the missing words.

For example, perhaps the voters are ANGRY (which would require the ruling party to shore up its standing)
Or perhaps the voters are UNDECIDED/UNCERTAIN (which would require the ruling party to shore up its standing)

So, among the answer choices, A, C, D and F are all legitimate answers.
At this point, we must remember the directions for all Sentence Equivalence questions:

Select the two answer choices that, when used to complete the sentence,
fit the meaning of the sentence as a whole and produce completed sentences that are alike in meaning.

So, for example, if it were the case that answer choice A (aloof) is correct, then we'd need a second word
(among the answer choices) that is SYNONYMOUS with aloof.
Since there is no such similar word, we can ELIMINATE A

What about choice C (restive)? Is there a second answer choice that is SYNONYMOUS with restive?
YES! Answer choice D (skittish) is synonymous with restive.
So, C and D are great candidates.

What about choice F (vociferous)? Is there a second answer choice that is SYNONYMOUS with vociferous?
Since there is no such similar word, we can ELIMINATE F

Answer: C and D

Cheers,
Brent
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Answer is RESTIVE & VOCIFEROUS

Aloof - is being left out / alone / isolated

as the ruling part is besieged with Charges it's obvious the Electorate won't have a peaceful ambiance so Reject Tranquil / Placid

sKITTISH - Is being Nervous or Scared off



Answer is Restive & Vociferous

Answer is indeed C and D, the sentence lacks the adjectives aka more clues for the blanks however IF WE FOCUS ON THE CONTEXT C) restive
D) skittish are patent answers because the even when the sanctity of clues -- the government -aka the ruling party has being embroiled "by charges that it trades favors for campaign money". No doubt the electorate aka voters are bond to be (my word for the bank--- NERVOUS)

HENCE
C) restive
D) skittish

Can someone explain how aloof and vociferous are relevant here?

Please Sir, see the explanation provided by our tutor greenlightprep.

There is not so much to add.

regards
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Answer choice D (skittish) is synonymous with restive.

restive (Choice C) and skittish (Choice D).