Jack must have been joking when he said that he was going to quit his job.为什么用when用what不行吗

写省略句（英语）1.Jack must have playing football and must have been doing her homework must have been done must have done must have/ must have been的区别 must not have been;could not have Jack described his father,who___a brave boy many years ago,as a strong-willed man.A.would be B would have been C must be D must have been.我最想问的是,为什么C Jack described his father,who___a brave boy many years ago,as a strong-willed man.A.would be B would have been C must be D must have been.我最想问的是,为什么C 一道单选must have been 和would have been的区别?Jack described his father, who _______a brave boy many years ago, as a strong–willed man A. would be B. would have been C. must be D. must have been 我不能理解为什么不能用would表示 must have been与must have done的区别? i think______(一定是）Jack that parked the car like that,for he is always doing so.为什么标答是it must have been Jack must have been joking when he said that he was going to quit his job.为什么用when用what不行吗 32 jack descried his father,who _____a brave boy many years ago,as a strong-wiled manA.would be B.would have beenC.must be D.must have been为什么 It Must Have Been Love (Cologne) 歌词 请问：有没有must have been? It Must Have Been Love 歌词 she kowns Jack well.She must have met him before must have been done/must be done求解两者异同 must be和must have been有什么区别he must have been sleeping.为什么这里要用must have been而不用must be be,must be,can't have been,must have been吗