There's no light on.they____be at home.为什么用can't,而不用mustn't.mustn't不是表推测吗?

There's no light on.they____be at home.为什么用can't,而不用mustn't.mustn't不是表推测吗?
There's no light on.they____be at home.
为什么用can't,而不用mustn't.mustn't不是表推测吗?

There's no light on.they____be at home.为什么用can't,而不用mustn't.mustn't不是表推测吗?
can't 是用于否定的推测.而must是用于肯定的推测的,mustn't用于关于禁止内容的句子.
1.That must be him.He said he would come yesterday.
2.That can't be her.She has gone to London.

mustn't 太肯定~推测时用CAN'T表示你的主观想法 他们不会在家

must的否定形式mustn't表示 不准，不许
can't 不可能

要表达"肯定不是某某人/什么物"就用
can't be
mustn't be表示"不准是..."