Everyone must be present at the meeting.情态动词后要用动词原形,所以是must

Everyone must be present at the meeting.情态动词后要用动词原形,所以是must must be是情态动词吗 must是情态动词吗? 情态动词后面加动词原形,为什么还可以是 he must have been away , 英语：must是情态动词吗?后面是不是用动词原形? MUST后要加动词原形? 情态动词need&must must 做情态动词后面接连系动词原形be再后面为什么要跟动名词形式? MUST既是情态动词又是助动词? have 和must是情态动词吗?是不是情态动词和助动词后面都跟动词原形?就是说第三人称单数也不需要加es了? 高中情态动词题1,your sister must be at home,_______she?A,isn't Bdoe 情态动词must的问题