一道语法题请教[求助]

amo

5. 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
我听课时发现：白永在解释D时说that没有指代对象
但我觉得that就是在指代前面的rate啊？

donna

这里的D问题很多，two times  不够简洁
还有that的指代是有问题，比较结构有问题。

2love2live

答案什么啊？

donna

答案是C

2love2live

I got 'c' too out of a hunch, but are all others wrong because  we can't use fast, faster, greater to modify 'rate', besides other awkwardnesses?