问题描述:

---Why didn’t youanswer my phone when I phoned you at about 11 p. m. yesterday?---I ________ andfailed to hear the phone.A.might havesleptB.must besleepingC.might besleepingD.must havebeen sleeping

网友答案:
D解析虚拟语气。用must have done表示对情况的推测,排除BC。表示昨天11点时的正在进行的动作,应该用进行时态,排除A。
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