问题补充：
---John, how did your English exam go?
-----I thought I ,but in fact I came in the top 10% in the class.
A. should have failed
B. couldn’t have failed
C. might have failed
D. mustn’t have failed
答案：
A. should have failed
B. couldn’t have failed
(答案→)C. might have failed
D. mustn’t have failed
解析：句意：我本以为我可能会失败。Might have done表示对过去的一种推测；A项意为“本应该做而实际未做”；B项意为“不可能”；D项表示禁止。
【标签】情态动词表推测
