before的详细用法

Before 在英语中是一个比较常用的虚词,它既可作介词或副词用,也可作从属连词用.在近几年的高考试题中常常出现考查其从属连词用法的题目.下面就把其作为从属连词的用法归纳如下：
1.表示“在…..之前就…..”.
Mary had finished her homework before her mother returned.
2.表示“过了多久后才……..,动作进行到什么程度才……”
The man almost knocked me down before he saw me .
They walked about 30 miles to the west before they saw a village .
They worked day and night about three days before everything returned to normal .
3.表示“来不及； 尚未…..就…”
Before I could get in a word ,he had measured me .
He ran off before I could stop him .
She left the company before I could have a word with her .
4.表示“刚…就…”
I had hardly sat down before the bell rang.
5.表示“不知不觉就…..； 还没弄清就……”
Time passed quickly and three months went by before Aqiao knew it.
6.表示“宁愿…,决不…,与其…,毋宁….”常与will 或would 连用.
I would die before I would tell
I’d shoot myself before I apologized to him.
I would / will die before I surrender .
7.表示“否则；以免”
Do it now before you forget .I will write it down before I forget it .
8.用于句型“it was +时间段+ before …” 表示 “过了多久才…”
It was three days before he came back..
9.用于句型 “ it was not long +时间段+ before …” 意为“不久就….”
It was not long before he sensed the danger of the position .
10.用于句型“it will be(not )+时间段+ before….”表示“要过多久/ 不久…才…”
It will be half a year before you graduate from this school .
It will be not long before you find you are wrong .