There's no light on.they____be at home.A:can't B:mustn't C:needn't D:shouldn't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.A:can't B:mustn't C:needn't D:shouldn't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.
A:can't B:mustn't C:needn't D:shouldn't
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.A:can't B:mustn't C:needn't D:shouldn't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,不允许内容的句子.
1.That must be him.He said he would come yesterday.
2.That can't be her.She has gone to London.

can't be 表示不可能，不会，语气要比mustn't更强烈
多做题就知道了 这种题是最常见的

mustn't表示"禁止? 而 can't 表推测