which must have been taken before level 2 course

which must have been taken before level 2 course must have been done must have done must have/ must have been的区别 there are courses which must have been taken before levl 2这句话怎么翻译 尤其是have been taken 359.1 must not have been;could not have which countries have you been? must have been与must have done的区别? In a country which must certainly have been a long way away from where we Romanians live.怎么译? It Must Have Been Love (Cologne) 歌词 请问：有没有must have been? It Must Have Been Love 歌词 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 must have been doing与must have been done都表示推测,有什么区别呀? must have been请问 must have been 是推测某人一直在做某事吗? i think he must have been a mechanic,中的must和have been是什么词啊? may have been和 must have been been是不是不仅表示被动?