一道prep语法题

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 projections.

(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 it 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，请问D错在哪里？是would和they were吗？这里不是虚拟语气，所以would错；they指代carbon emissions in 2010而不是carbon emissions in 1990，所以错误吗？

不知道我的理解对不对呢？

level是单数，显然只有that可以，如果用those，那只能指 carbon emissions ，比较对象不对