两道GMATprep.上的改错题，请教NN

if current trends continue, by the year 2010 carbon emissions in the United States will soar to a level more than one-third higher than were those in 1990, according to official projiections.

A. will soar to a level more than one-third higher than were those
B. will soar to a level more than one-third higher than that
C. would soar to a level more than one-third higher than is was
D. would soar to a level more than one-third higher than those
E. would soar to a level more than one-third higher than they were

正确答案是B，不明白的是carbon emissions是复数，为何可以用that指代？

The success of the program to eradicate smallpox has stimulated experts to pursue what they had not previously considered possible--better control, if not eradication, of the other infections such as measles and yaws.

A. what they had not previously considerd possible--better control, if not eradication, of the other infections such as

B. what they had not previously considered a possibility--better control, if not eradication, of such infections like

C. something they had not previously considered possible--better control, if not eradication, of such infections as

D. something not considered a previous possibility--better control and perhaps eradication, of other infections such as

E. the possibility of what they had not previously considered--better control and possibly eradication of infections like

正确答案是C，不清楚的地方有两点：一，在这句句子里用what作persue的宾语是否可以？

二，smallpox（天花）是infections的一种，那么当在列举其他infections，如measles和yaws的时候，infections前面为什么不用加other?

请大家各抒己见，谢谢！

Good questions.

In the first question, "that" means "level", not "emissions".

In the second question, I believe "what" can replace "something"

The problem of choice A comes from "of the other infections." The word "the" is not needed b/c it makes the sentence confusing.