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?