晕了晕了，大全一题

1.        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（C）

(E) two times greater than

答案是C，但是不明白的是C中twice what it was in的it指代问题。按照PREP语法笔记当中，it指代的应该是the rate of increase in 1980，如果这样的话这个it应该是不正确的，不知道理解对不对？求教

一般不用two times