must be和must have been 在句子中作什么成份及其时态?must be算是must+系动词么?如果后面加doing就算是现在进行时?must have been 本身可以算是现在完成时么?如果后面加doing就算是现在完成进行时么?是

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must be和must have been 在句子中作什么成份及其时态?
must be算是must+系动词么?如果后面加doing就算是现在进行时?
must have been 本身可以算是现在完成时么?如果后面加doing就算是现在完成进行时么?
是不是可以理解为must为助动词,而其后不论是be还是have been,其本身的功能与时态并不受must的影响和改变,仅仅是因为加了must而多了一层肯定性的推测意义?

must be不一定是系动词,后面加doing是现在进行时.
must have been 本身可以是现在完成时,后面加doing是现在完成进行时

must 是情态动词,意思是必须,表推测时为“一定,后面加任何动词都行。
you must be careful. 你一定得小心。
must be doing:肯定某人正在做某事..He must be doing his homework.他一定在做他的作业
must have been doing:肯定某人一直在做的事..He must have been tryin...

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must 是情态动词,意思是必须,表推测时为“一定,后面加任何动词都行。
you must be careful. 你一定得小心。
must be doing:肯定某人正在做某事..He must be doing his homework.他一定在做他的作业
must have been doing:肯定某人一直在做的事..He must have been trying his best to study..他肯定一直都在尽力学习..
must have been 是对推测的一种肯定。

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