title: 给我讲一下before的用法吧，越多越好，最好能与since比较? 
desc: 给我讲一下before的用法吧，越多越好，最好能与since比较。
answer: 后接“时间点”，可用于任何时态，如： 
  
  　　She got  to  his    before 5'o clock. 
  　　她５点钟以前就到了办公室。 
  
  单独使用，常与现在完成时连用，也可与一般过去时连用，如： 
      I have never met him before.
  　 我以前从未见过他。
  
  也可放在表“时间段”的词语后，与过去完成时连用，表示从过去某时刻算起的若干时间以前，如： 
      He said he had finished his job 2 days before.
  　　他说他两天前就完成了他的工作。
   
  
  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。
  
  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 .
  
  
  