can't have been,must have been 结构里是不是不要把have been当现在完成时看,就把它当成一个结构来使用?

be,must be,can't have been,must have been吗 can't have been和can' have done有什么区别或者must have been和must hane done;may have been和may have done can't have been和must have been每一个的用法 She can't have been Danish. and She must have been Swedish. must have been和can't have been和现在完成时有没有联系啊 用must have been/done或can*t have been/done 改写句子 He can't find his key.He ---------- them.A.must lost B.must have been lost C.must have lost he can't haue been a dcntist.he must have been a doctor.翻译下 He can't have been.He must have been.不是说单三用has吗?这里怎么用的have? can't have been,must have been 结构里是不是不要把have been当现在完成时看,就把它当成一个结构来使用? I think they were Canadian.I don't think they were.They can't have been Canadian.They must have been Australian.帮我看看有无语法错误 英语：助动词的问题he must（can't may等） have been asleep,就有两个助动词,must ,have,很少见哦,还有没有其他的情况 Greens must have been to Shanghai ,_____they?A.hadn't B.didn't C.can't D.weren't还有haven‘t they I think she was old.我认为她原来是老的?I don't think she was.She can't have been old.She must have been young.这怎么翻译I think it was cheap.I don't think it was.It can't have been cheap.It must have been expensive.同上.最好将语 用can't have been造句! 有must/could/can/may/maight have been done吗 I can't get though to the general manager's office anyhowThe line is busy.Someone__the phone.A.must useB.usesC.must have been usingD.must it have been是B，为什么？ They can't have been watching the football match this time yesterday,___?A.must theyB.can theyC.have theyD.were theywhy choose