【题目】_______ carefully before you hand in your paper please.
A.Checking
B.Check
C.To check
D.Checked

【答案】B
【解析】考查祈使句。句意：交卷之前请认真检查。before引导的是时间状语从句，前面的祈使句是主句，动词用原形。故选B。