must have done,must do,can't have done,can't do的区别

must have done对过去发生的动作很有把握的肯定推测
must do“必须做”,含有一种命令的口吻,语气强
can't have done对过去发生的动作很有把握的否定推测,意为“不可能做了”
can't do“不能做”表示不给予许可,语气没有must do强