一、must +现在完成时 表示对已发生的事情的一种肯定的猜测。
1、Mr. Green _____ my letter, otherwise he would have replied before now.
A. must have received B. must have failed to receive C. must receive D. must fail to receive
2、I believe he _____ an accident, otherwise he would have arrived on time.
A. would have had B. could have had C. should have had D. must have had (答案为D)
二、should (ought to )+完成时 表示应该做的事情而没有做，否定式表示不该做的事情做了。含有对过去的动作的责备、批评。
1、They have done things they ought _____.
A. not to do B. not to be done C. not to have done D. not having done (答案为C)
2、I’m sorry I couldn’t get in touch with him before he left, I _____ him earlier.
A. had a telephone B. have phoned C. should have phoned D. should be phoned (答案为C)
三、could +完成时 表示能做的事情而没有做。表示对过去能做而未做的事情感到惋惜，遗憾。
1、He could have joined us, but he didn’t get our invitation in time. 他本来能够参加我们的，但是他没有收到我们的请贴。
2、I could have passed, but I did not study hard enough. 我本来能及格的，但是没有努力学习。
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