This is an evidence question. The argument is that, because of the various benefits that go to oil companies and road maintenance, the "true price" of gas is supported by the government. This means that drivers of inefficient vehicles aren't paying their fair share. We're looking for a choice that has an outcome that would either strengthen or weaken the argument (that is, "evaluate the argument").

(A) This is irrelevant to the comparison between high- and low-mileage vehicles.
(B) This is related to the topic at hand, but not very directly. The amount spent on gas depends not only on gas efficiency, but also on number of miles driven. Since we don't know whether high- or low-mileage vehicle drivers drive more miles, we can't evaluate the argument with this bit of information.
(C) This is off-topic, though it does relate to things in the argument. It doesn't matter how oil companies make their money--the point is that, thanks to government support, the price of gas is lower than it would otherwise be.
(D) This is correct. The argument is essentially claiming that the benefits of those "hidden costs" are to the advantage of inefficient vehicle drivers. If we knew whether some of those benefits really were accruing to certain types of drivers, we would be better able to evaluate the argument.
(E) This is irrelevant--the argument is about how certain governmental policies affect the price of gas, not whether the listed mechanisms are the only ways it does so.