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首先请看2006年高考一道题:
_______environmental damage is done, it takes many years for the ecosystem(生态系统) torecover. (2006江苏卷31)
A. Even if B. If only
C. While D. Once
解析: 答案为D｡even if“即使”,if only “要是……就好了”,while“虽然”, once“一旦”｡句意为“一旦环境遭到破坏,就要花很多年才能恢复生态系统”,故D正确｡once作连词表示“一旦,只要”,引导条件状语从句｡再如:
Once you understand the rules of the game, you will enjoy it.一旦你了解了游戏的规则,你就会喜欢它｡
Once he is free, he will play computer games. 只要他有空,他就玩电脑游戏｡
条件句的表达形式常见的还有:
1. if如果
You should call 119 if there’s a fire.
If you think that treating a woman well means always getting her permission for things, think again. (06湖南)
2. unless如果不,除非(多数情况下与if...not用法相同,两者都引导条件状语从句,但unless比if ... not的语气要强｡)例如:
Unless you have tried it, you can’t imagine how pleasant it is. (06北京)
You will be lateyou leave immediately.
A. unless B. until C. if D. or
答案A｡句意: 除非你立即走,否则你会迟到的｡该句可转化为 If you don’t leave immediately, you will be late. B､D项填入后句意不对,or表转折,若用or则句子应为: Leave immediately or you will be late. 再如:
He is sure to come unless he has some urgent business. = He is sure to come if he hasn’t any urgent business.
注意: 当unless引导的从句的主语与主句的主语相同时,unless后面的主语和动词有时可省略｡
Unless (he is) in uniform, he doesn’t look like a policeman.除非他穿着制服,否则他看起来不像警察｡
He will not come unless (he is) invited.除非被邀请,否则他是不会来的｡
但在下列情况下要斟酌替换使用:
1) 当从句是虚拟形式时,只用if ... not,不用unless引导｡例如:
The flowers would have died if you had not watered diligently.
2) 当主句为疑问句时,不用unless,而用if ... not｡例如:
What shall we do if he doesn’t reply to our letter?
3) 当unless引导的从句带有否定词时,不能用if ... not代替｡例如:
I’ll go unless no one else goes.
3. as long as只要
As long as there is life there is hope. 有生命就有希望｡(留得青山在,不怕没柴烧｡)
I’ll accept any job as / so long as I don’t have to get up early.只要不必早起,任何工作我都可以接受｡
4. 祈使句或名词短语 + and+ 含有一般将来时或情态动词的陈述句_______, and I’ll get the work finished. (06重庆)
A. Have one more hour
B. One more hour
C. Given one more hour
D. If I have one more hour
Don’t be discouraged._______things as they are and youwill enjoy every day of your life. (2003上海春季)
A. Taking B. To take
C. Take D. Taken
_______blood if you canand many lives will be saved. (2001 上海春季)
A. Giving B. Give
C. Given D. To give
注意: 本句型可以和“if引导的条件句+主句”相互转换,它在高考中出现过｡例如:
_______your composition carefully, some spelling mistakes can be avoided.(1999上海)
A. Having checked B. Check
C. If you check D. To check
析: 本句可转化为: Check your composition carefully, and some spelling mistakes can be avoided.在复习时要注意类似的“祈使句 + or / or else / otherwise +含有一般将来时或情态动词的陈述句”句型｡例如:
Don’t mention that at the beginning of the story, or it may give away the shocking ending. (2003北京高考)
【练一练】
1. Once_______by heart, these sentencesare easy to write.
A. learning B. having learnt C. learnt D. being learnt
2. If_______, the iron will become soft.
A. being heated B. having been heated C. heated D. heating
3. _______closer, or you’ll not see itclearly.
A. Coming B. To come C. Come D. Having come
4. _______for the worst in advance andyou won’t be disappointe D.
A. Prepare B. When preparing C. Having prepared D. If you prepare
5. _______out in the forest, he will easily get lost.
A. Once B. Unless C. If D. Even if
Keys: 1. C 2. C 3. C 4. A 5. A
_______environmental damage is done, it takes many years for the ecosystem(生态系统) torecover. (2006江苏卷31)
A. Even if B. If only
C. While D. Once
解析: 答案为D｡even if“即使”,if only “要是……就好了”,while“虽然”, once“一旦”｡句意为“一旦环境遭到破坏,就要花很多年才能恢复生态系统”,故D正确｡once作连词表示“一旦,只要”,引导条件状语从句｡再如:
Once you understand the rules of the game, you will enjoy it.一旦你了解了游戏的规则,你就会喜欢它｡
Once he is free, he will play computer games. 只要他有空,他就玩电脑游戏｡
条件句的表达形式常见的还有:
1. if如果
You should call 119 if there’s a fire.
If you think that treating a woman well means always getting her permission for things, think again. (06湖南)
2. unless如果不,除非(多数情况下与if...not用法相同,两者都引导条件状语从句,但unless比if ... not的语气要强｡)例如:
Unless you have tried it, you can’t imagine how pleasant it is. (06北京)
You will be lateyou leave immediately.
A. unless B. until C. if D. or
答案A｡句意: 除非你立即走,否则你会迟到的｡该句可转化为 If you don’t leave immediately, you will be late. B､D项填入后句意不对,or表转折,若用or则句子应为: Leave immediately or you will be late. 再如:
He is sure to come unless he has some urgent business. = He is sure to come if he hasn’t any urgent business.
注意: 当unless引导的从句的主语与主句的主语相同时,unless后面的主语和动词有时可省略｡
Unless (he is) in uniform, he doesn’t look like a policeman.除非他穿着制服,否则他看起来不像警察｡
He will not come unless (he is) invited.除非被邀请,否则他是不会来的｡
但在下列情况下要斟酌替换使用:
1) 当从句是虚拟形式时,只用if ... not,不用unless引导｡例如:
The flowers would have died if you had not watered diligently.
2) 当主句为疑问句时,不用unless,而用if ... not｡例如:
What shall we do if he doesn’t reply to our letter?
3) 当unless引导的从句带有否定词时,不能用if ... not代替｡例如:
I’ll go unless no one else goes.
3. as long as只要
As long as there is life there is hope. 有生命就有希望｡(留得青山在,不怕没柴烧｡)
I’ll accept any job as / so long as I don’t have to get up early.只要不必早起,任何工作我都可以接受｡
4. 祈使句或名词短语 + and+ 含有一般将来时或情态动词的陈述句_______, and I’ll get the work finished. (06重庆)
A. Have one more hour
B. One more hour
C. Given one more hour
D. If I have one more hour
Don’t be discouraged._______things as they are and youwill enjoy every day of your life. (2003上海春季)
A. Taking B. To take
C. Take D. Taken
_______blood if you canand many lives will be saved. (2001 上海春季)
A. Giving B. Give
C. Given D. To give
注意: 本句型可以和“if引导的条件句+主句”相互转换,它在高考中出现过｡例如:
_______your composition carefully, some spelling mistakes can be avoided.(1999上海)
A. Having checked B. Check
C. If you check D. To check
析: 本句可转化为: Check your composition carefully, and some spelling mistakes can be avoided.在复习时要注意类似的“祈使句 + or / or else / otherwise +含有一般将来时或情态动词的陈述句”句型｡例如:
Don’t mention that at the beginning of the story, or it may give away the shocking ending. (2003北京高考)
【练一练】
1. Once_______by heart, these sentencesare easy to write.
A. learning B. having learnt C. learnt D. being learnt
2. If_______, the iron will become soft.
A. being heated B. having been heated C. heated D. heating
3. _______closer, or you’ll not see itclearly.
A. Coming B. To come C. Come D. Having come
4. _______for the worst in advance andyou won’t be disappointe D.
A. Prepare B. When preparing C. Having prepared D. If you prepare
5. _______out in the forest, he will easily get lost.
A. Once B. Unless C. If D. Even if
Keys: 1. C 2. C 3. C 4. A 5. A