[原创]比较问题~that/it was 分不清

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. (B)

(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

答案是通过条件状语主句将来时，从句现在时判断的.

但是如果将C 中的would 改为will ，是否正确呢？

但是如果将C 中的would 改为will ，是否正确呢？ 我觉得不正确。原文应该是：

by the year 2010 carbon emissions in the United States
                will soar to a level more than one-third higher than （the level）in 1990

C中多了一个was。但是，B中的that和C中的it都可以指代the levl么？that 和it的指代有什么区别么？

还望nn赐教

it/they通用名词是不带限定修饰成分的通用概念,不论何时何地都是它,

that/those具体名词则相反,指代具体事物且通常带介词结构等修饰成分,修饰成分不同则指代的事物不同.换了时间地点也不同

PREP破解中有提到：

that 是的指代名词前的修饰成分

it 指代 主句的主语>主句的宾语>从句的主语>从句的宾语

如果主句的主语是有修饰成分的名字，那么it 是可以指有修饰成分的名词的啊~~

请nn指点