问题补充：
------I don’t know why he has made such a silly mistake in the exam.
------ He it before he handed in the paper.
A. may have checked
B. might check
C. must have checked
D. should have checked
答案：
A. may have checked
B. might check
C. must have checked
(答案→)D. should have checked
解析：考查情态动词+have done的用法：A. may have checked可能已经检查了，B. might check 可能检查了， C. must have checked一定检查了，D. should have checked 本该检查而没有，句意是：--我不知道为什么他在考试中犯了这么愚蠢的错。--他本该交试卷钱检查一下的。选D。
