一、可以用作介词⒈)指时间上早于，在……之前，如：She has lived here since before the war.她从战前就一直在这儿住。⒉)指位置在前面，如：We knelt down before Grandma's grave.我们在奶奶的墓前跪下。⒊)指顺序或排列在之前，如：Your name comes before mine on the list.名单上你的名字在我之前。⒋)在某人面前，如：She said it before the witness.他是当着证人的面说的。二、作为连词其基本含义是“在……之前”，又可以根据不同语境灵活翻译成“才”、“还没来得及就……”、“趁……”、“就”等。具体用法如下：⒈)与情态动词can/could连用这时候从句虽为肯定形式，根据汉语表达习惯译成“还没来得及就”，如：Before I could get in a word，he had measured me.我还没来得及插话他就为我量好了尺寸。Before she could move，she heard a loud noise，which grew to a terribl eroar.她还没来得及迈步，就听见一声巨响，接着就是可怕的隆隆轰鸣。⒉)用于肯定句中强调主句所表达的时间，距离长，或花费的精力大，译成“才”We had sailed four days and four nights before we saw lands.我们航行了四天四夜才看到陆地。We waited a long time before the train arrived.我们等了很长时间火车才到。⒊)用于否定句中，强调主句所表达的时间，距离短，或花费的精力小，译成“不到……就”如：We hadn't run a mile before he felt tired.我们跑了还不到一英里他就累了。⒋)主句含有hardly，scarcely等半否定副词时可以译为“刚……就”这时候主句应用过去完成时态，从句用过去时，还可以用when替代before如：We had scarcely reached the school before/when the bell rang.我们刚到学校铃声就响了。⒌)有时还有“宁愿”的意思I'd shoot myself before I apologized to him.我宁死也不向他道歉。⒍)用于It+be/take+时间段+before句型在这一句型中又可以根据主从句的时态分成两种情况。若主句是一般时将来时态，从句是一般现在时.若主句是肯定句意思是“要过多长时间才”；若主句是否定形式翻译成“用不了多久就”。It will be two weeks before everything returns to normal.两周之后一切才能恢复正常。It will be many years before the situation improves.这种状况或许要过许多年才能得以改善。It won't be long before we meet again.用不了多久我们就会再见面的。这时若主句是一般过去时从句也是一般过去时。若主句是肯定句翻译成“多长时间之后才”，若主句是否定形式翻译成“没过多久就”。如：It was some time before I realized the truth.过了很长一段时间我才了解到真相。It wasn't long before she became a brave solider.没过多久她就成了一名勇敢的战士。After that it still took seven years before they got married.他们又过了七年才结婚。注意：当主句的谓语动词为延续性动词时，before与until有时可以互换。It was an hour before/until the police arrived.
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