A growing number of the decisions made at federal, state, an

In sentence correction questions, the first thing that I prefer to do is a vertical scan of all the answer options. Most of the time you will able to find a 2/3 split among these 5 options.

Here you can see that we can split the options into two groups.
1 group containing 3 options with the verb "involves" (A, B and C).
And the second group containing 2 options with the verb "involve" (D and E).

If you are able to do a 2/3 split then this will help you in eliminating the wrong options fast.
As "A growing number of the decisions" is a plural subject and its matching plural verb "involve" is present only in options D and E. So at this point we can instantly eliminate A, B and C.

Out of D and E, E is wordy and awkward. Moreover GMAT doesn't prefer the use of being.

Hence the only option available is D.

Okay, my mistake was that I assumed that "number" is singular, but it seems to be generally plural at least according to Grammar Monster.

"The number" is always singular
"A number" is always plural.

Two splits:
1. A number of followed by compound subjects...thus the verb should be plural 'involve' instead of singular 'involves'. This eliminates A, B, and C.
2. 'knowledgeably challenge' ...the decisions are not incapable of knowledgeably challenging, the electorates are, hence option D.

With 2 things u can answer this question.

First of all, "A x number of something" means plural of something. If "THE" had been used then the subject would have been singular. So subject should pick plural verb, which is "involve". This eliminates A,B and C. And in E, you see "being" is not used as a noun or as a verb in indirect speech. So E is also out, leaving us with only D as the answer.

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Here subject resides in quantitative prepositional phras"Growing number of decision" and this is plural subject and hence takes plural verb 'involve'.

That modifier refers to technical judgements

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