英语情态动词区别

题目

英语情态动词区别
There's no light on-they______be at home.为什么用can't 而不是 mustn't?
You ___ play computer games before you finish your homework.是用mustn't 还是shouldn't?
请说一下can't,mustn't 和shouldn't的区别,最好再举几个例子,

答案

must表示不必要,而cant表示不可能,而shouldn't表示不应该,灯没亮,人则不可能在屋里,第二句就当然是should‘nt