在be to do中不定式作表語，be to do主要用法和含義包含以下四個方面，一起來學習一下吧！
1、be to do ...可以用於第一人稱疑問句中，表示徵求對方意見。如：
Am I to go on with the work？
要我繼續這項工作嗎？
What are we to do next？
我們下一步該怎麼辦？
What is to be done?
應該怎麼辦呢?
2、表示按約定、計劃，或按職責、義務、要求等即將發生的動作，這是將來時的一種用法。這種用法最為常見和普遍，也最應該掌握。如：
They are to pay a visit to the teacher together at 10 a．m. tomorrow.
他們約定明天上午10點一起去看這位老師。
We are to meet at the station at four this afternoon.
我們今天下午4點在車站見面。
When are you to leave for home?
你什麼時候回家?
She is to be married next month.
她將於下個月結婚.
The Queen is to visit Japan in a week’s time.
女王將於一週後訪問日本.
3、表示必須或應該，在意義上等於must，should，ought to 或have to。如：
You are to finish the work before five this afternoon.
你們必須在今天下午五點以前完成這項任務。
This medicine is to be taken three times a day.
這種藥一天要服三次。
The letter is to be handed to him in person.
這封信必須親手交給他。
You are to do your homework before you watch TV.
看電視之前你得先做完作業。
4、用來表示註定要發生或不可避免要發生的事。如：
His theory was to change the views on the universe.
他的理論勢必要改變(人類)對宇宙的看法。
I felt nervous because I was soon to leave home for the first time.我感到很緊張,因為我很快就要首次離開家了。
They said goodbye,little knowing that they were never to meet again.他們告了別,不知道以後再也不會見面了。
5、用於否定句,表示“禁止”,相當於mustn’t.例如：
The books in this room are not to be taken outside.
這個室內的書籍不得帶出室外。
You are not to smoke in the reading-room.
你不可以在閱覽室裡吸菸。
6、表示“可以,可能”,相當於may,can.例如：
The news is to be found in the evening paper.
這條消息可以在晚報上見到。
Such people are to be found everywhere.
這種人到處都有。
She is nowhere to be found.
在哪裡也找不著她。
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