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本文结合典型例题来归纳一下before的特殊用法。
before作为连词时的基本意义是“在……之前”，用于表示时间或顺序。如：Turn the light off before you sleep. (睡前先把灯熄掉。) Think before you speak. (说话之前，应先想清楚。) 但在不同的语境中before有不同的意义：
1． before表示“不等……就……”、“尚未……就……”
例1： —Why didn’t you tell him about the meeting？ (2006年四川)
—He rushed out of the room_____ I could say a word.
A. before B. until C. when D. after
解析： 答案为A。题中before意为“不等……就”、“尚未……就……”，它表示从句的动作尚未来得及发生，主句的动作已发生或完成。全句句意为：我还没来得及说他就冲出了房间。又如：
Before I could get in a word, he had measured me.我还没有来得及插上话，他就给我量好了尺寸。
The phone stopped ringing before I answered it.我还没有来得及接，电话就挂了。
2． before表示“不知不觉，还没弄清就……”(常用于before sb. know／realize…)
例2： Several weeks had gone by_____ I realized the painting was missing. (2004全国)
A. asB. before C. since D. when
解析： 此题最易错选C或D项，而正确答案为B。用since则时间延续到了现在，在时间上与had gone矛盾；用when则无法强调时间流逝的不知不觉性。又如：
Time passed quickly and three months went by before I knew it.时间飞快地流逝，不知不觉3个月过去了。
3． before表示“以免，不然”
例3： It’s cloudy. Take an umbrella_____ you regret it.
A. but B. and C. after D. before
解析： and及but表示并列关系，不合语境；after意为“在……之后”，不合常识，应是在下雨前带伞；before在此处意为“以免你后悔”。before作此意义的用法的例子不少，又如：
Put that away before it gets broken.把它收好，以免砸了。
Do it before you forget.尽早动手，不然忘了。
4． before用于it was / will be ＋ 时间 ＋ before ... 句型中。
例4： It won’t be long_____ you regret what you have done.
A. after B. before C. since D. until
解析： It was / will be ＋ 时间 ＋ before ... 表示“过了多久才…(强调时间的长)”，在否定句中则表示“没过多久就…(强调时间的短)”。例如：
It will be two years before we meet again.我们要过两年才能见面。
It wasn’t long before he married again. 不久他就又结婚了。
We didn’t wait long before he came back. 我们没等多久他就回来了。
5． before表示“与其……宁可……，比……优先”(用于表优先顺序)
例5： They would fight to death_____ they surrendered(投降)．
A. before B. after C. since D. because
解析： 答案为A。before引导的从句在与will, would连用时，有“宁愿……也不”的含义。before即使是作介词用也有此意义。例如：
True men choose death before dishonor. 大丈夫宁可杀不可辱。
I’d die before I apologize to them! 我宁死也不愿向他们道歉！
We will die before we give in.我们宁死不屈。
6. before表示“……才”（强调从句动作发生得晚或慢）
例6： They sailed along the Pacific Ocean for two weeks_____ they arrived home.
A. since B. when C. before D. after
解析： 此题正确答案为C。全句句意为：“他们在太平洋航行了两个星期才回到家。”强调从句动作比主句动作发生晚。又如：
I thought carefully about it before I made a decision.我经过再三考虑才决定。
It may be many years before the situation improves.或许要过很多年这种状况才能得到改善。
【巩固性练习】
1. A scientist must practise_____ he can use all data(数码) tools well.
A. as soon as B. when
C. until D. before
2. The next moment,_____ she realized wha was happening, she was hit over the head.
A. when B. before C. since D. as
3. —Why didn’t you help the little boy?
—Oh, sorry. He had struggled to his feet__________ I ran over.
A. until B. after C. before D. since
4. He made a mistake, but then he corrected the situation_____ it got worse.
A. until B. when C. before D. as
5. Scientists say it may be 5 years or 6 years__________it is possible to test this medicine on human patients.
A. since B. after C. before D. when
6. Someone called me up in the middle of the night, but theyhung up_____ I could answer the phone.
A. as B. since C. until D. before
7. You’d better give it up_____ it is too late as it’s very dangerous.
A. since B. before C. as D. when
8. It would be months_____ he was fit for work.
A. until B. since C. before D. after
9． It was evening_____ we reached the little town of Winchester.
A. that B. until C. since D. before
10． The scientists had tried out thousands of chemicals_____ they found the right one.
A. since B. after C. before D. when
Keys: 1． D2． B3． C4． C5． C6． D7． B8． C9. D10. C
before作为连词时的基本意义是“在……之前”，用于表示时间或顺序。如：Turn the light off before you sleep. (睡前先把灯熄掉。) Think before you speak. (说话之前，应先想清楚。) 但在不同的语境中before有不同的意义：
1． before表示“不等……就……”、“尚未……就……”
例1： —Why didn’t you tell him about the meeting？ (2006年四川)
—He rushed out of the room_____ I could say a word.
A. before B. until C. when D. after
解析： 答案为A。题中before意为“不等……就”、“尚未……就……”，它表示从句的动作尚未来得及发生，主句的动作已发生或完成。全句句意为：我还没来得及说他就冲出了房间。又如：
Before I could get in a word, he had measured me.我还没有来得及插上话，他就给我量好了尺寸。
The phone stopped ringing before I answered it.我还没有来得及接，电话就挂了。
2． before表示“不知不觉，还没弄清就……”(常用于before sb. know／realize…)
例2： Several weeks had gone by_____ I realized the painting was missing. (2004全国)
A. asB. before C. since D. when
解析： 此题最易错选C或D项，而正确答案为B。用since则时间延续到了现在，在时间上与had gone矛盾；用when则无法强调时间流逝的不知不觉性。又如：
Time passed quickly and three months went by before I knew it.时间飞快地流逝，不知不觉3个月过去了。
3． before表示“以免，不然”
例3： It’s cloudy. Take an umbrella_____ you regret it.
A. but B. and C. after D. before
解析： and及but表示并列关系，不合语境；after意为“在……之后”，不合常识，应是在下雨前带伞；before在此处意为“以免你后悔”。before作此意义的用法的例子不少，又如：
Put that away before it gets broken.把它收好，以免砸了。
Do it before you forget.尽早动手，不然忘了。
4． before用于it was / will be ＋ 时间 ＋ before ... 句型中。
例4： It won’t be long_____ you regret what you have done.
A. after B. before C. since D. until
解析： It was / will be ＋ 时间 ＋ before ... 表示“过了多久才…(强调时间的长)”，在否定句中则表示“没过多久就…(强调时间的短)”。例如：
It will be two years before we meet again.我们要过两年才能见面。
It wasn’t long before he married again. 不久他就又结婚了。
We didn’t wait long before he came back. 我们没等多久他就回来了。
5． before表示“与其……宁可……，比……优先”(用于表优先顺序)
例5： They would fight to death_____ they surrendered(投降)．
A. before B. after C. since D. because
解析： 答案为A。before引导的从句在与will, would连用时，有“宁愿……也不”的含义。before即使是作介词用也有此意义。例如：
True men choose death before dishonor. 大丈夫宁可杀不可辱。
I’d die before I apologize to them! 我宁死也不愿向他们道歉！
We will die before we give in.我们宁死不屈。
6. before表示“……才”（强调从句动作发生得晚或慢）
例6： They sailed along the Pacific Ocean for two weeks_____ they arrived home.
A. since B. when C. before D. after
解析： 此题正确答案为C。全句句意为：“他们在太平洋航行了两个星期才回到家。”强调从句动作比主句动作发生晚。又如：
I thought carefully about it before I made a decision.我经过再三考虑才决定。
It may be many years before the situation improves.或许要过很多年这种状况才能得到改善。
【巩固性练习】
1. A scientist must practise_____ he can use all data(数码) tools well.
A. as soon as B. when
C. until D. before
2. The next moment,_____ she realized wha was happening, she was hit over the head.
A. when B. before C. since D. as
3. —Why didn’t you help the little boy?
—Oh, sorry. He had struggled to his feet__________ I ran over.
A. until B. after C. before D. since
4. He made a mistake, but then he corrected the situation_____ it got worse.
A. until B. when C. before D. as
5. Scientists say it may be 5 years or 6 years__________it is possible to test this medicine on human patients.
A. since B. after C. before D. when
6. Someone called me up in the middle of the night, but theyhung up_____ I could answer the phone.
A. as B. since C. until D. before
7. You’d better give it up_____ it is too late as it’s very dangerous.
A. since B. before C. as D. when
8. It would be months_____ he was fit for work.
A. until B. since C. before D. after
9． It was evening_____ we reached the little town of Winchester.
A. that B. until C. since D. before
10． The scientists had tried out thousands of chemicals_____ they found the right one.
A. since B. after C. before D. when
Keys: 1． D2． B3． C4． C5． C6． D7． B8． C9. D10. C