they must feel really worried,don' t they?

问题描述:

they must feel really worried,don' t they?
为什么不是 mustn’t they?
老师有说过must be 是 用be动词反意疑问
must do 用 动词的反意疑问

mustn't是禁止的意思而不是“肯定不”的意思
所以如果要表否定要用can't
情态动词的否定都用can't