这是怎么回事？？？？？？ 帮忙！！！ 急！

16.   (27621-!-item-!-188;#058&003223) 

Most of the world's supply of uranium currently comes from mines.  It is possible to extract uranium from seawater, but the cost of doing so is greater than the price that uranium fetches on the world market.  Therefore, until the cost of extracting uranium from seawater can somehow be reduced, this method of obtaining uranium is unlikely to be commercially viable.

Which of the following would it be most useful to determine in evaluating the argument?

(A) Whether the uranium in deposits on land is rapidly being depleted

(B) Whether most uranium is used near where it is mined

(C) Whether there are any technological advances that show promise of reducing the cost of extracting uranium from seawater

(D) Whether the total amount of uranium in seawater is significantly greater than the total amount of uranium on land

(E) Whether uranium can be extracted from freshwater at a cost similar to the cost of extracting it from seawater

 答案a 但是结论是：Therefore, until the cost of extracting uranium from seawater can somehow be reduced, this method of obtaining uranium is unlikely to be commercially viable  a明显不是在评价这句结论阿.... 他说的是另一个方法on land

20.   (28411-!-item-!-188;#058&003617)

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.

 答案c 明显加强的是：so damage to Palitito's buildings from the buses' exhaust will diminish significantly. 所以几个与bus exhaust无关的选项就排除了...

 到底应不应该 把握住结论阿？？？？？？？？？？

 通常作题都是根据结论 找答案... 但是 第一道题似乎 说明了我的方法不对....

 帮帮忙~~~

20.   (28411-!-item-!-188;#058&003617)

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.

 答案c 明显加强的是：so damage to Palitito's buildings from the buses' exhaust will diminish significantly. 所以几个与bus exhaust无关的选项就排除了...

 到底应不应该 把握住结论阿？？？？？？？？？？

 通常作题都是根据结论 找答案... 但是 第一道题似乎 说明了我的方法不对....

 帮帮忙~~~