A) Who cares about regular automobiles? We are only concerned about buses and parking spots here. It's a trap choice because the GMAT is trying to shift your thinking towards alternative causes of pollution; a type of thinking handy on many other CR questions. If we can assume other things won't make the problem worse, we would have reason to believe this plan might work, but this is exactly the type of thinking the GMAT is tricking you with here, since the prompt says the buildings are damaged by buses, and thus cars don't matter here.

B) Whether other pollution harms these buildings or not does not matter as well, since the plan seeks to reduce damage from buses and not other sources. Pretty easy one to eliminate.

D) Also may be a trap answer for some test-takers. D confirms the idea that buses constitute the majority proportion of tourist traffic. Either way, this does not support the city's plan that parking will reduce bus pollution. Whether buses are 99% of all tourist traffic or 51%, this has no bearing on the fact that additional parking will reduce current pollution levels.

E) Okay, this is probably the trickiest and most appealing trap answer choice here. Here's why it's a trap- E states that some of the buses that can't find parking are gonna just drive around polluting the city with reckless abandon, so you think great, additional parking will definitely reduce pollution because these buses would be parked instead of driving around. But here's the thing, what would those buses that can't find parking do instead? They are either going to idle around, polluting the city anyway. E doesn't actually change anything about what we already know of this world. E is in fact, describing a scenario that is, in terms of pollution output, fundamentally the same as what is already written in the prompt. We already know parking is limited, and that buses idle around because of this. Whether they drive around or idle around makes no difference to the level of harm the buildings will experience. So it doesn't really support the plan, E is rather neutral.

C) THE CORRECT ANSWER! Whew, we made it guys! Let's look at why C definitely is the correct answer. C says buses spend less than one-quarter of the time transporting people around from site to site. So the rest of the time, the MAJORITY of the time, these buses need to find somewhere to park or they will just idle around. The prompt says parking is limited though, so most of the time these buses are damaging buildings by idling at the curb. If a third of these buses are now able to find parking, you'd have good reason to believe the pollution to buildings will decrease, thereby strengthening the logic of the prompt. It is also important to note that C says the majority of the time is spent idling, since parking is the alternative to idling; thus, buses will actually spend a lot of time parked and therefore not polluting.