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

Answer 1

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。