Hello!

The national infrastructure for airport runways and air traffic control requires immediate expansion to accommodate the increase in private, smaller planes. To help fund this expansion, the Federal Aviation Authority (the FAA) has proposed a fee for all air travelers. However, this fee would be unfair, as it would impose costs on all travelers to benefit only the few who utilize the new private planes.

Which of the following, if true, would cast the most doubt on the claim that the proposed fee would be unfair?

This is a type of weakening question. We need to find out which statement helps us to weaken the above conclusion(Highlighted in red).

(A) The existing national airport infrastructure benefits all air travelers.- As the existing benefits the traveler, they won't require expansion and the fees they pay would be a waste, strengthens- OUT
(B) The fee, if imposed, will have a negligible effect on the overall volume of air travel.--Same as A- OUT
(C) The expansion would reduce the number of delayed flights resulting from small private planes congesting runways.--I can keep this one as it would be of some benefit for the other passengers
(D) Travelers who use small private planes are almost uniformly wealthy or traveling on business.--Absolutely strengthens.- Out
(E) A substantial fee would need to be imposed in order to pay for the expansion costs.---I was a bit dicey about this one, but, I rejected this because we are looking for something that weakens and not a neutral statement.

Thus, IMO C

Do let me know if there is something wrong with my reasoning!! I'd appreciate that!!