辨析be to do，be going to do，和be about to do的区别

be to do，be going to do，和be about to do的区别为：含义不同、用法不同、侧重点不同。

一、含义不同

1.be to do

释义：要做的事。

例句：

I assure you that she can be trusted to do the job. 

我担保她能做好这项工作。

2.be going to do

释义：将要做的。

例句：

I'll be hanged if she's going to do that! 

我绝不会让她那样做！

3.be about to do

释义：准备好了。

例句：

If I were you I'd be thinking about what to do with that information.

如果我是你，就会想想该怎么办。

二、用法不同

1.be to do

用法：事先商定、安排或准备要做的事情。

2.be going to do

用法：将要发生的事情或打算最近要进行的动作。

3.be about to do

用法：即将发生的动作，在时间上指最近的将来。

三、侧重点不同

1.be to do

解析：表示可能性，必要。

2.be going to do

解析：在含有条件状语从句的主从复合句中，主句一般不用be going to，而常用will。

3.be about to do

解析：不能再加时间状语。

辨析be to do, be going to do, be about to do
1) be to do:
(1)表示事先商定、安排或准备要做的事情。如：
The students are to meet at the school gate tomorrow. 明天学生们将在学校大门口集会。
2）表示可能性，必要、责任、义务、禁止等。如：
Her necklace was not to(couldn't)be found. 她的项链找不到了。
2) be going to do:
1) 表示将要发生的事情或打算最近要进行的动作。如：
It is going to rain soon. 快要下雨了。
2) 在含有条件状语从句的主从复合句中，主句一般不用be going to，而常用will（第一人称用shall）。如：
The football match will be put off if it rains tomorrow. 如果明天下雨，足球赛将被推迟举行。
3) be about to do:
1) 表示即将发生的动作，在时间上指最近的将来。如：
We are about to start. 我们就要出发了。
The new school year is about to begin. 新学年开学在即。
2) 在含有be about to do的句子中，不能再加时间状语。如：
Wrong: The medical team is about to start immediately.
Right: The medical team is about to start. 医疗队就要出发了。

附：be to do 用法的详细讲解：
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.
I was to play Juliet.
The expedition was to start in a week’s time.
was/ were to have done, 表示 “本打算”、“本计划”或“本应当” 做的事而没有做成或没有发生。如:
I was to have seen him last Wednesday, but he didn’t come.
We were to have been married last year.
2. 表示 “义务”、“应该” 。(意思接近于should， must， ought to， have to) 如：
No one is to leave the building. 谁也不得离开这楼房。
You are not to smoke in this room.=You are not supposed to smoke in this room.
You are to be back by 10 o’clock. 你必须十点以前回来。
3. 表示可能性, 相当于can, may 如:
Such books are to be found in the library. 这样的书在图书馆里就能找到。
Not a single sound was to be heard. 一点儿声音也听不到。
Not a soul was to be seen. 看不到一个人影。
She was nowhere to be found. 哪儿也找不到她。
She was never to see his wife and family again.
5. 表示 “命运”, 将来必然要发生的事, 译作 “注定……”。如：
He came to power, but he was to play dearly for it: soon he was assassinated.
The worst is still to come.
They said goodbye, little knowing they were never to meet again.
6. 用于“if…were to do”，表示虚拟语气。如：
If it were to rain tomorrow, the sports meeting would be put off. 如果明天下雨, 运动会就会延期。

Exercises:
1.This film _____ this Sunday.
A. is going to show B. is showing C. is to be show D. will have been show
2.The students were told that they ____ at the school gate at 2:00 the following afternoon.
A. met B. will meet C. were to meet D. were met
3. The house ______ ready today but as there has been a builders’ strike it is still only half finished.
A. is B. was to be C. was D. was to have been
4.In such dry weather, the flowers will have to be watered if they _________.
A. have survived B. are to survive C. would survive D. will survive
5.How _______ I ______ what has become of him?
A. am; to know B. am; knowing C. was; to know D. will; know
6. ______ he ________ tomorrow, I would go to meet him at the station.
A. Were; to come B. Was; coming C. Did; come D. Would; come

be going to do
将会...
一般用于将来时态

例句与用法:
1. I am assuming that the present situation is going to continue.
我认为目前的情况将会继续下去.

2. It's going to cost 200 or as near as dammit.
这要花200英镑上下.

3. How did you find out that Burns was going to be promoted?
你是怎么知道伯恩斯将会得到提升的？

4. You must be out of your mind if you think I'm going to lend you 50!
你以为我会借给你50英镑, 你准是疯了!

5. I'm just going to check in these books at the library.
我要去图书馆还这些书。

6. They are going to move to a new house next week.
下星期他们将迁入新居。

7. It looks as if it is going to rain.
看来要下雨了。

8. Are you going to America by boat or by plane?
你到美国是坐船还是坐飞机？

.be to do

表示安排、计划、决定、命令或注定要发生的事.
一般用于被动语态，，，to be done
也可以用于主动语态。。。都是表示将来时态

比如：
Greater efforts to increase agricultural production must be made if food shortage is to be avoided.
为避免食物短缺，我们需要更加努力来提高农业生产。

The bridge is to be built next year.
大桥将在明年修建。

以下是主动语态的例句：
He is to die.
他就要死了。

To live is to work.
活着就要工作。

比较：
I am to be an engineer.
我就快要成为工程师了。。（这个时间上快一点，而且比较有把握，比如已经考到证了。。）

如果是：
I am going to be an engineer.
意思就变成了：
我将成为工程师。。。（这个只是主观愿望。没有多少把握）

4.be about to do
表示即将，马上要做的事，。，

这个比其他的几个都要紧迫。。
比如：
I am about to leave.
我马上就要离开了。（刻不容缓，就是这一两分钟的事）
比较：
I am going to leave.
我将要离开。（还指不定是什么时候）

5.be doing

主要用于现在进行时态，，有时可以用来表达将来时

例句与用法:

How are you doing with your new boss?
你跟你的新上司处得如何？

We are doing a pilot study to see if the new product will sell well.
我们正在为这种新产品做试销调查，看它的销路好不好。

According to these figures, our company is doing well.
从这些数字来看，我们的公司经营得不错。

be to do是指按计划或正式安排将发生的事。
be going to do表示将来发生的某事。
be about to do马上要进行的动作也就是非常近的，将来往往不与表示将来的时间状态连用。

呵呵娇滴滴记得记得就