Premise:
In order to raise revenue, the federal government planned a tax amnesty program that
allows tax delinquents to pay all owed tax without added financial penalty.

Conclusion:
However, economists projected that the federal government would collect a far lower percentage of total tax owed by delinquents than did state governments implementing similar programs.

Which of the following, if true, would most contribute to an explanation of the
economists’ projections?

So we want to strengthen the argument that if the federal governemnt implements the same program they will collect lower taxes than what the state government did.

So before looking at the questions think for a second what you need. The answer should show why people would pay back more state taxes then they would federal taxes.

If you alread have this in mind before looking at the answers then you wont get distracted easily.

A. Tax amnesty programs are only successful if they are widely publicized.

Does this give a reason why people would pay back state tax but not federal tax? No, so move on.

B. Most people who honestly pay their state tax are equally honest in paying their
federal tax.

This addresses people paying state and federal tax but it argues the opposite and weakens.

C. Although federal tax delinquents usually must pay high financial penalties, the
states require far lower financial penalties.

The fees will be abolished so this is irrelevant.

D. The state tax rate varies considerably from state to state, but the federal tax is
levied according to laws which apply to citizens of all the states.

Doesn't address why people would pay more of one over the other.

E. Unlike most federal tax delinquents, most state tax delinquents fail to pay state
tax because of an oversight rather than a decision not to pay.

Bingo! The people who do not pay their state tax do so because they forget not because they were unwilling. These peopel would surely pay once they are reminded and given the opportunity to do it penalty free. It also implies that dont pay federal tax do so because they intentionally dont want to. These people are far less likely to repay once penalties are removed because they didn't want to pay in the first place when there were no penalties.

If you already have an ideal of what your looking for it is easier to spot in a crowd than if you just go through them one by one and decide if they make sense or not.