请问有be to do的用法吗?什么意思?

一般说来，“be to do”这个结构有两种语法意义，其一是连系动词be+动词不定式做表语，其二是be to是一个独立词汇单位,具有情态含义,可以把它叫做情态习语(modal idiom)。

一、be +动词不定式,不定式做表语,表示主语和表语在概念上是等同的。如：

The problem is to find a solution.

His plan is to clean the room.

My wish is to be a doctor.

二、be to +动词不定式中的be to用作情态习语,这时的be to do表示: “计划”、“安排”、“义务”、“应该”、“可能”、“命运”等。(have to, ought to)。如:

He is to have a holiday. (表示将来)

The committee is to meet today. (表示计划、安排)

You are to go to the hotel where rooms have already been booked for you.

1.表示“将”、“计划”、“安排”。(意思接近于be going to)如：

Their daughter is to get married soon.

Who is to question him？

It was the last film at the cinema，which was to close next day.

After dinner they were to go to a movie.

was/ were to do表示过去曾经计划要做的事，或者过去应当做的事，而且从现在的角度来看已经实现了。如：

I felt nervous because I was soon to leave home for the first time.