同学你好，该知识点来自沪江网校《英语初级进阶【微信专享班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好：
1.  He must be a teacher. 他一定是名教师。
2. He can't be a teacher. 他不可能是一名教师。
3. He was in hospital yesterday, he must has been ill.
  他昨天在医院，一定是病了。
4. He can't have been at home, he has been in America for three years.
  他不可能在家，他已经去美国三年了。


希望以上答案可以帮助到同学！
祝愿同学学习进步！