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be going to +动词原形;shall/will + 动词原形;be + to do(动词原形);be about to do(动词原形);be +doing (现在分词)。
1. will/ shall do表示单纯的将来，或临时要做某事。
will用于各种人称，shall一般用于第一人称，但是will表示将来通常不用于状语从句中，而用一般现在时代替。
Which paragraph shall I read first？ 我先读哪一段呢？
I’ll tell him the truth if I see him tomorrow.如果我明天看到他，我就告诉他实情。
You said Tom is ill?I’ll go to see him now.
你说汤姆病了？我现在马上去看他。
注意：在if引导的条件状语从句中可以用will表示主语的意愿。
If you will listen to me, I’ll tell you the truth.如果你愿意听我说，我就告诉你实情。
2. be going to指现在的打算、意图，表示最近的计划和安排。
be going to可以表示计划、安排要做的事，也可表示有迹象表明最近的将来要发生的事。
Also I’m not going to ask you what words mean.(2015浙江高考)
我也不打算问你们单词是什么意思。
What are you going to do this weekend?你这周末打算干什么呢？
It is going to rain, sowe’d better stay indoors.要下雨了，因此我们最好待在室内。
3. be doing与表示将来的时间连用，表示不久的将来计划要发生的事或动作。
When are you going off for your holiday?你什么时候去度假？
Are you staying here till next week?你会在这儿呆到下周吗？
4. be to do表示按预定计划或安排要发生的事情，还可以表示“注定”、“可能性”、“义务”等。
He is to have a holiday.他要度假了。
You are to pay for your fault.你得为你的失误付出代价。
We are to discuss the report next Saturday.我们下星期六讨论这份报告。
You are to go to the hotel where rooms have already been booked for you.
你要去那家旅馆，房间已经给你预定了。
5.一般现在时表示将来。分为三种情况：
1）按照规定（如工作计划、各种时刻表）要发生的未来的动作，仅限于go, come, leave, start, stay, return, begin等等。
The train leaves ten minutes later.火车十分钟后启动。
Here comes the bus. = The bus is coming.车来了。
2）用于时间状语从句（when, unitl，...）、条件状语从句（if，unless，...）等，代替will表示的一般将来时。
I’ll write to you as soon as I arrive there.我到了那里，就写信给你。
3）在动词hope, take care that, make sure that等的宾语从句中。
I hope they have a nice time next week.我希望他们下星期玩得开心。
Make sure that the windows are closed before you leave the room.
离开房间前，务必把窗户关了
6. be about to do刚要，正要，表示非常近的将来。
1)be about to不能和表示将来的时间副词连用。
2)be about to do... when ...正要……的时候……事情发生了。
He is about to leave for Beijing.他马上要去北京。
She was about to dish up when some guests came.
她刚要上菜开饭，这时来了一些客人。
As she was about to speak, I frowned her down.
她刚要开口，我就皱皱眉示意她别出声。
I was about to go swimming when my guide shouted at me and told me not to do so.
我正要去游泳，这时向导大声叫我不要去。