OFFICIAL EXPLANATION

In this Explain the Paradox problem, the paradox is that sales were up 10% but the airport saw that as "low sales," enough to fire the company that presided over that increase. Here a savvy examinee might start predicting reasons: what if sales should have been up quite a bit more than 10%? You're looking for a reason (maybe rampant inflation) that a 10% increase in sales did not keep up with what would have been the expected increase. And choice D provides that: if the airport was 30% busier overall, then you would have expected sales volume to be in the 30% increase range holding all other variables the same. So a 10% increase did not keep pace with expectation.

Of the incorrect choices: choice A brings in a comparison that is largely irrelevant. Since you do not know the starting points of each airport (that 15% increase could have been from a historic low) you cannot conclude that this airport's 10% increase was "bad" just from the comparison. Choice B also brings in an irrelevant point, as the stimulus clearly states that "low sales" was the SOLE reason for replacing vendors.

Choices C and E, at least to some extent, somewhat justify a low sales increase. If C were true, then that might suggest that more people would wait to eat on the plane and not eat at the airport. In that light, even a small sales increase could be seen as a good thing, making the decision to fire the vendor seem less justified. Even more so, E performs the same function: if there were fewer points of sale for much of the year but an overall increase, one would think that the increase of 10% would likely increase again for the next year and make firing the vendor seem like a poor move.