MUST 后面的时态
问题描述：
MUST 后面的时态
E.g.The teacher said,“John,you must bring your book to the class
=The teacher told John that he must bring his book to the class.
第2句的MUST,后面的BRING用的是一般现在时,那是不是MUST后面的动词一定用一般现在时（原型）啊?
答
must是一个情态动词.情态动词本身有时态的变化,但是情态动词后面跟的动词必须是动词原形.