20.
For years the beautiful Renaissance buildings in Palitito have been damaged by exhaust from the many tour buses that come to the city. There has been little parking space, so most buses have idled at the curb during each stop on their tour, and idling produces as much exhaust as driving. The city has now provided parking that accommodates a third of the tour buses, so damage to Palitito's buildings from the buses' exhaust will diminish significantly.
Which of the following, if true, most strongly supports the argument?
(A) The exhaust from Palitito's few automobiles is not a significant threat to Palitito's buildings.
(B) Palitito's Renaissance buildings are not threatened by pollution other than engine exhaust.
(C) Tour buses typically spend less than one-quarter of the time they are in Palitito transporting passengers from one site to another.
(D) More tourists come to Palitito by tour bus than by any other single means of transportation.
(E) Some of the tour buses that are unable to find parking drive around Palitito while their passengers are visiting a site.
为什么C选项能起到支持作用呀？我选的B。。。请教各位牛人～ | 
