问几个英语短语的区别

***be going to do：你要去做这件事，而且很快就要做
例子：I'm going to study hard this winter so that I can pass my exams in the summer.

be to do的主要2个用法：
***be about to do：你要去做这件事，就现在(比going to do急）
例子：I'm sorry sir, you can't come in now because I'm about to close my shop

***be to do: 你要去做这件事,意思和be going to do相近.be to do表示: '计划", "安排", "义务", "应该", "可能", "命运"等。
例子：The committee is to meet today.

***be to do 还表示主语和表语在概念上是等同的.be +动词不定式, 不定式做表语.
例子:His plan is to clean the room.

意思上无法区别，只能从搭配上来说：
be about to do 不与确切的时间壮语连用，经常用与 sb be about to do when +句子中
be going to do是计划打算将要做

be to do" 的5 种用法   a) 表示“按计划、安排即将发生某事或打算做某事”。 例：She is to be seen in the lab on Monday.（星期一你准会在实验室见到她。） b) 该做或不该做的事情（语气上接近于should, must, ought to, have to），表示一种命令、规劝性语气。 例：You are to go to bed and keep quiet, kids. Our guests are arriving in less than 5 minutes.