—She looks very happy. She have passed the exam—I guess so. It’s not difficult after a

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A. should
B. could
(答案→)C. must
D. might
解析：    
试题分析: 句意：——她看上去非常开心。她肯定通过考试了。——我认为是这样。考试一点也不难。must have done “肯定做过某事”是对过去发生事情的肯定推测，might have done和 could have done表示“可能做过某事”；should have done“本应该做但是没做”，根据句意判断C选项正确。