Question

If you ___ be in time for the early bus,be sure to get up before five o'clock in the morning.

A.are to
B.are about to
C.will D.are due to答案选的A,为啥呢？？请详细解答

Answer 1

be to do sth表示表示按计划或安排要做的事；或者表示“必须”“应该”“打算”做某事。意愿性比较明显。
be about to do sth即将做某事；打算做某事。这个短语有时与be to do sth可以互换，但是它的意愿性没有be to do sth那么明显。
will do sth将做某事
be due to sth.由于某事
句意：如果你想赶上早班车，那就必须在五点钟以前起床。
根据句意，是计划、打算做某事。

Answer 2

be to be 在这句话里表示打算，相当于want
be +动词不定式（即be + to do sth.）的用法如下：
1.表示按计划或安排要做的事。例如：
When are you to leave for home?你什么时候回家？
She is to be married next month.她将于下个月结婚。
The Queen is to visit Japan in a week’s time.女王将于一周后访问日本。
这种结构也可用于过去。was / were to do sth. 表示曾经计划要做的事，但不表明计划是否被执行，或表示“命运（即命中注定要发生的事）”，而非计划；was / were to have done sth.表示未曾实现的计划。例如：
I felt nervous because I was soon to leave home for the first time.我感到很紧张，因为我很快就要首次离开家了。
They said goodbye, little knowing that they were never to meet again.他们告了别，不知道以后再也不会见面了。
We were to have told you, but you were not in.我们本来想告诉你的，但是你不在家。
2.表示“应该”，相当于should, ought to。例如：
You are to report to the police.你应该报警。
What is to be done?应该怎么办呢？
3.表示“必须”，相当于must, have to。例如：
The letter is to be handed to him in person.这封信必须亲手交给他。
You are to do your homework before you watch TV.看电视之前你得先做完作业。
4.表示“想，打算”，相当于intend, want。例如：
If we are to be there before ten, we’ll have to go now.如果我们要在十点前到，我们现在就得走。
5.用于第一人称疑问句，表示征求对方意见。例如：
Am I to go on with the work?要我继续完成这项工作吗？
What are we to do next?我们下一步该怎么办？
6.用于否定句，表示“禁止”，相当于mustn’t。例如：
The books in this room are not to be taken outside.这个室内的书籍不得带出室外。
You are not to smoke in the reading-room.你不可以在阅览室里吸烟。
7.表示“可以，可能”，相当于may, can。例如：
The news is to be found in the evening paper.这条消息可以在晚报上见到。
Such people are to be found everywhere.这种人到处都有。
She is nowhere to be found.在哪里也找不着她。
8.were to do sth.用于if或even if / even though从句中，表示对未来的假设。例如：
If I were to tell you that I killed him, would you believe me?要是我告诉你是我杀了他，你会相信吗？
Even if the sun were to rise in the west, I would never do such a thing.即使太阳从西边出来，我也决不做这种事。
9.be to blame(该受责备，对某坏事应负责任)与be to let(待出租)两种结构中，用不定式的主动形式表示被动含义。例如：
Which driver is to blame for the accident?这事故是哪个司机的责任？
This house is to let.这房子要出租。
Exercise
1. We have been looking for the boy all the afternoon but he is nowhere _____.
A. to see B. seeing C. seen D. to be seen
2. As early as his second film, Chaplin had developed his own manner of acting, the one that ___ world famous.
A. would become B. became C. was to become D. had become
3. ----We just saw John at the bookstore.
----That’s strange; I didn’t think he ____ back until tomorrow.
A. will come B. was to come C. is coming D. is to come
4. The final examination ___early July.
A. is to be held B. is to be taken place
C. is going to hold D. will be to take place
5. If the sun ___ tomorrow, what would we do?
A. were not to raise B. does not rise
C. would not rise D. were not to rise
6. A new hospital was to ____ in this district, but the money wasn’t collected yet.
A. have been built B. be built C. built D. have built
7. Look at these clouds. ____.
A. It’s going to rain B. It’s raining
C. It is to rain D. It can rain
8. Who do you think ____ for the failure of their marriage.
A. to blame B. to be blame C. is to blame D. is to be blamed
9. Neither you nor he ____ to the front.
A. are to be sent B. is to be sent C. have to be sent D. is to send
10. I ____ to bed when there was a knock at the door.
A. went B. am going to C. was to go D. was about to go
11.----____ we ____ again next week?
----Yes, let’s make it next Wednesday.
A. Are; to meet B. Shall; be to meet
C. Will; meet D. Are; meeting
12. As students, we ____.
A. won’t smoke B. are not to smoke
C. aren’t smoking D. don’t smoke
Key: 1.D 2.C 3.B 4.A 5.D 6.A 7.A 8.C 9.B 10.D 11.A 12.B