How will the right answer fit in terms of support and conclusion?

Only the right answer will support disagreeing with the conclusion.

Highlight the main conclusion in the passage, if there is one:

The government’s tax collection agency has not followed through on its plan

[CONCLUSION], [BACKGROUND]. [SUPPORT], and [SUPPORT].

Map the wording of the answers to the wording of the passage:

(A) …part of a broad campaign against corporate misconduct.

This doesn’t tell us anything about whether the government has “followed through on its plan”, which is especially clear since there’s no info in this answer about what’s happened “over the past year”.

(B) The number of personal income tax returns…

…is totally irrelevant, since the passage only talks about “corporate” income taxes.

(C) Most audits…do not reveal any significant violations.

Like (A), this doesn’t tell us anything about whether, “over the past year”, the government has or hasn’t “followed through on its plan” to crack down.

(D) It generally takes longer than one year to complete an audit…

Aha! This is the only answer that maps directly to the wording used in the argument. If the plan was only “announced a year ago”, then this answer tells us that it’s too soon for an audit to be completed. In that case, the last sentence of the passage doesn’t actually support the conclusion that the government “has not followed through on it plan”.

(E) Over the last five years, fewer audits…

This is changing the timeframe from the passage, which makes it impossible to tell whether the government “has not followed through on its plan” “over the past year”.

(D) is the correct answer.