I have passed my examination easily, but I made too many stupid mistakes.
A. must
B. will
C. shall
D. could
网友回答
A. must
B. will
C. shall
(答案→)D. could
解析：考查虚拟语气。根据but后面句中的过去式可知这个虚拟语气是与过去事实相反。四个选项中只有D可以用于虚拟语气。Could have done本可以做某事；句意：我本可以很容易地通过考试，但是我缺犯了很多愚蠢的错误。