请教语法题"In the 1980’s the rate of increase of the minority population of the Unite

E9—45 In the 1980’s the rate of increase of the minority population of the United States
was nearly twice as fast aS the 1970’s．
(A)twice as fast as
(B)twice as fast as it was in
(C)twice what it Was in
(D)two times faster than that of
(E)two times greater than

答案是C。

记得高中学语法的时候，what引导的从句，what本身在从句中充当一定的成分。刘继民说it 指the rate of increase，那么what指什么呢？该怎么理解"what it was"这个表达？

谢谢。

 what在定语从句中相当于先行词(即要修饰的名词)+定语从句的连接词 

在这个句子中what=the rate of increase that

the rate of increase 做前面twice的表语，that则引导后面的定语丛句

what=the thing that

what 和 something that的意思上有差距，前者的意思表明说话人确定是什么，而后者只表示有那样一个东西 ，不确定是什么。

what it was中was 是the rate of increase，what it was可以看成the thing that the rate of increase was，就是1970年代的增长率，没有重复。

另外，对于玻璃胶带的解释，我觉得it这里不是形式主语。形式主语的真正主语在后面，一般是it is ... that或it is ... to do形式，而如本题所示的句子我认为仅仅是普通的主系表结构，it是普通的代词。

open to discussion

恩...同意GmatThunder的解释.