请教一道语法题目

megy666

5. The current downturn in the U.S. economy is encouraging many young professionals to return to school, which doubles to twice the number of applicants five years ago.

A.      which doubles to twice the number of applicants five years ago

B.      doubling to twice the number of applicants five years ago

C.      which doubles to twice the number of applicants that were five years ago

D.      doubling to twice the number of applicants five years before

E.      which doubles to twice the number of applicants five years before

iamwuyan

选撒? B? 这题的考点应该是不能用WHICH指代前半个句子