You should study harder it is too late to catch up.A. ifB. whenC. afterD. before

问题补充：

You should study harder it is too late to catch up.

A. if

B. when

C. after

D. before

答案：

A. if

B. when

C. after

(答案→)D. before

解析：if是否，如果；when当……时；after在……之后；before在……之前，以免。句意：你应该努力学习，不然太晚了，就来不及了。故选D。