1表示事先安排或要做的事
we are to visit the industrial exhibition next week.
2 表示可能，多用于否定句和疑问句
how is he to buy so expensive a coat?
the book is to be borrowed from our school library.
3表示应该做某事
the college students are to be required to become both red and expert.
4表示必须
the traffic regulations are to be observed.
5表示禁止
these new instruments are not to be taken out of the laboratory.
6表示事态发展的结果或不可避免
he died in a car accident and was never to see his unborn son.
7 表示目的
the letter was to tell him that he had no time to spare.
8用于主语是第一人称的疑问句重征求别人意见
are we to discuss in class?
9用于条件句中表示打算和意图
if i were to go to BeiJing ,i would visit the Summer Palace.
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