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助动词be(am, is, are, was, were, being, been)的用法

(1) be后跟现在分词构成进行时态。

Who is playing the violin?谁在拉小提琴?

She was reading a book then.那时她正在读书。

(2)be后跟过去分词构成被动语态。

He was asked to do the work.有人要他干这件工作。

You are invited to attend the meetintg.有人邀请你参加会议。

(3)be 后跟不定式作谓语，有如下几种情况：

①表示计划、安排将要发生的事。

Who are we to meet?我们要见谁呀?

I'm to have supper with John this afternoon.今天下午我要与约翰一起吃晚饭。

②表示指示、命令，否定式表禁止。

You are to see the headmaster today.今天你必须去见校长。

You are not to enter the room without permission.未经允许你不能进入房间。

③表示义务、责任等，同should。You are to be back before 5.你得在5点钟以前回来。

What is to be done?该干什么。

④表示可能性，与情态动词may, can同义。

Such books are to be found in any library.这种书任何图书馆都有。

Not a sound was to be heard.一点声响也没有。

⑤表示后来发生的事，可以用来表示命运或注定

They say good-bye, little knowing that they were never to meet again.他们告别了，没想到再也不能相见了。He was to regret the decision.他有一天会后悔做出这一决定的。

⑥用于习语

Where am I to go? 我该向何处去?

What am I to do? 我该怎么办?