before的时态怎么判断
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。
具体用法
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. .