摘要：1．表示对过去事实的推测.常用于否定句和疑问句. He can't couldn't have watched TV yesterday for he knew they would have an exam. 昨天他不可能看电视.因为他知道快要考试了. I don't know why she didn't call me yesterday. Can she have forgotten my telephone number 我不知道昨天她为什么没给我打电话.难道她会把我的电话号码忘了吗? He didn't come to school yesterday. Can he have been ill 他昨天没来学校.难道他生病了?

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