白勇书209页的一道小题

In the 1980's the rate of increase of the minority population of the United States as nearly twice as fast as the 1970's.

b. twice as fast as it was in

c. twice what it was in

我觉得B看起来更爽一点,为什么C对?B又错在哪里?

谢谢

b. (the rate was) twice as fast as it was in

c. (the rate was) twice what it was in

I think it is not right to say that "the rate is fast"