为什么have done也可表示持续到现在的动作或 状态例如My mother has taught English for twenty years那他和have been doing 表示持续到现在的动作或 状态有什么区别?

为什么have done也可表示持续到现在的动作或 状态例如My mother has taught English for twenty years那他和have been doing 表示持续到现在的动作或 状态有什么区别? i have seen the film before请问这句话为什么用现在完成?看电影 这个动作在之前 又不是持续到现在?为什么用have done? would have done,might have done,could have done,should have done分别表示什么意思? have+sth.+done表示什么意思 请问HAVE SB DONE 不表示现在完成时 have sth to be done/have sth done?为什么要用have anyting to be done? having done和to have done区别?我们老师说regret to have done,forget having done都表示完成. must have done 和 should have done 的表示推测区别?must have done 和 should have done 都表示推测时,区别是什么? may have done might have done区别He___you more help.even though he was very busy 为什么不能用may have done呢?may have done 不也能表示过去的推测吗?...关键是他说要用might have done我想问下。 must have done 表示猜测 那 must do 表示什么 请问could not have done/might not have done可用于虚拟语气中吗 we have done much为什么用much you have done me a great service.为什么用have done,为什么不用have been 情态动词+have done 如 could have done,must have done,should have done 等等在如他么的否定词表示什么意思? could have done能不能表示对过去事实的猜测用在肯定句中?与must have done may have done might have done May not have done 是表示可能不还是不可能 那Could not have done呢 could only have done表示对过去的推测,只可能...,是否等于must have done? 英语非谓语动词 有人这么说 to do不定式表示将来发生的动作,Having done一般是指已经持续了一段时间的动作,后面一般都有表示一段时间的短语,像for an hour啊since breakfast啊之类的；to have done 一