同学你好，该知识点来自沪江网校《中小学金牌新概念英语第三册【升级班】》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。

同学你好哦~
be +动词不定式(即be + to do sth.)的用法如下:
1.表示按计划或安排要做的事。例如:
When are you to leave for home?你什么时候回家?
The Queen is to visit Japan in a week’s time.女王将于一周后访问日本。


这种结构也可用于过去。was / were to do sth. 表示曾经计划要做的事，但不表明计划是否被执行，或表示“命运(即命中注定要发生的事)”，而非计划;was / were to have done sth.表示未曾实现的计划。例如:
I felt nervous because I was soon to leave home for the first time.我感到很紧张，因为我很快就要首次离开家了。
They said goodbye, little knowing that they were never to meet again.他们告了别，不知道以后再也不会见面了。


2.表示“应该”，相当于should, ought to。例如:
You are to report to the police.你应该报警。
What is to be done?应该怎么办呢?

3.表示“必须”，相当于must, have to。例如:
The letter is to be handed to him in person.这封信必须亲手交给他。
You are to do your homework before you watch TV.看电视之前你得先做完作业。

4.表示“想，打算”，相当于intend, want。例如:
If we are to be there before ten, we’ll have to go now.如果我们要在十点前到，我们现在就得走。
祝同学学习愉快~