105　be about to do sth. 和be to do sth.

① be about to do sth.表示“正要做某事，马上要做某事”，主语一般是人，时间距离很近（immediate future），后面不可跟表示将来时间的状语，如soon，at once，immediately。be about to do 后还常跟when 从句，相当于just at this time，也可以是 was doing…when（正在做……这时），had done…when（刚刚做……这时）。

I was just about to leave when the telephone rang. 我正要离开时，电话铃响了。

I was writing a letter when the light went out. 我正在写一封信，这时灯熄灭了。

We had just started our work when the machine broke down.我们才刚刚开始工作，这时机器就坏了。

I was walking down the road when a bird flew past overhead. 我正在路上走着，这时一只鸟从头顶上飞过。

They are about to leave soon.

They are about to leave.

他们就要动身了。

② be+to do sth.表示预先的安排或计划，也表示命令、指示、劝告等。主语一般是人，有时可以是物。

The foreign friends are to arrive this evening. 外国朋友定于今天晚上到达。（安排）

Father is to return next month. 父亲将于下个月回来。（计划）

The plan is to be made in a week. 计划将在一周内做好。（计划）

You are not to walk on the grass. 不许践踏草坪。（命令）

You are to be criticized if you do like that. 你那样做就会受到批评。（警告）

All the exercise-books are to be handed in after class. 所有的练习本都必须在课后交上来。（要求）

She was to have left earlier，but it rained. 她本打算早些离开的，但是却下雨了。

提示

①be to do sth. 用于第二人称时，有时表示“应该，理应”的含义，相当于should。

You are to give her more help. 你应该给她更多的帮助。

You are to study harder. 你应该更努力地学习。

②be to do sth. 也可以是表语结构。

Her duty is to keep the hall clean and tidy. 她的职责是保持大厅整洁。

One of the most urgent things to do now is to get enough money. 现在要做的最紧迫的事情之一是弄到足够的钱。