"条件"表达法是中学英语中相当重要的语法现象,对"条件"表达法的了解,同学们不能只停留在"if"引导的"条件"句上。实际上,"条件"表达法的意义相当广泛,为了使同学们更好地复习和了解"条件"表达法的考点和用法,本文拟就"条件"表达法的考点及相关知识归纳如下。

　　一、考查"when, if, unless"引导的条件句的用法

　　典型题例

　　①Don't be afraid of asking for help ______ it is needed.

　　A. unless B. since C. although D. when

　　②The WTO can't live up to its name ______ it does not include a country that is home to one fifth of mankind.

　　A. as long as B. while C. if D. even though

　　③You'll succeed in the end ______ you give up halfway.

　　A. even if B. as though C. as long as D. unless

　　解析:when, if, unless充当从属连词,其意义分别为"如果","除非、如果不"。如:When there is no gravity, our feet no longer stay on the ground.如果没有地球引力,我们就不可能站在地面上。You will be late unless you leave immediately.快点走吧,要不然你会晚的。

　　特别提示:在if, when, unless等引导的条件句中,应当注意时态的对应性。一般来讲,if引导的条件句常用一般现在时表将来,而主句常用一般将来时。如:If it doesn't rain tomorrow, we will hold the sports meet.如果明天不下雨,我们就开运动会。

　　真题回练

　　1. ______ your composition carefully, some spelling mistakes can be avoided.

　　A. Having checked B. Check

　　C. If you check D. To check

　　2. If city noises ______ from increasing, people ______ shout to be heard even at the dinner table 20 years from now.

　　A. are not kept; will have toB. are not kept; have to

　　C. do not keep; will have toD. do not keep; have to

　　3. The bell will ring ______ there is a fire.

　　A. even B. that C. if D. although

　　4. The man will have to wait all day ______ the doctor works faster.

　　A. if B. unless C. whether D. that

　　5. ______ he comes, we won't be able to go.

　　A. Before B. UnlessC. Where D. After

　　Key:1-5 CACBB

　　二、考查"in case"引导的条件句的用法

　　典型题例

　　I don't think I'll need any money but I'll bring some ______.

　　A. at last B. in case

　　C. once again D. in time

　　解析:本题考查in case引导的条件句的用法。in case引导条件句,其意义为"假使、以防(万一)"。

　　特别提示:1) in case的位置较为灵活,可置于从句的句首或句尾。其时态常用一般现在时表将来。2) in case引导的从句也可以用虚拟语气(should+动词原形)。

　　真题回练

　　1. John may phone tonight. I don't want to go out ______ he phones.

　　A. as long as B. in order that

　　C. in case D. so that

　　2. I shall stay in the hotel all day ______ there is news of the missing child.

　　A. in case B. no matter

　　C. in any case D. ever since

　　Key: 1-2 CA

　　三、考查"祈使句+and/then+陈述句"表示条件概念的用法

　　典型题例

　　One more week, ______ we will accomplish the task.

　　A. or B. so that C. and D. if

　　解析:在"祈使句+and/then+陈述句"这个结构中,前面"祈使句"相当于if引导的条件句,表示"要是……(就会)",表示该条件一旦实现,必然出现某一结果。但如果表示"该条件实现不了,会出现什么结果"时,则用"祈使句+or/or else/otherwise+陈述句"。如:Hurry up, or you will be late for class.快点儿,要不然上课就迟到了。

　　真题回练

　　1. ______ it with me and I'll see what I can do.

　　A. When left B. Leaning

　　C. If you leave D. Leave

　　2. ______ blood if you can and many lives will be saved.

　　A. Giving B. Give

　　C. Given D. To give

　　3. ______ some of this juice, perhaps you'll like it.

　　A. Trying B. Try

　　C. To try D. Having tried

　　Key:1-3 DBB

　　四、考查省略句中条件概念的表达法

　　典型题例

　　Unless ______ to speak, you should remain silent at the conference.

　　A. invited B. inviting

　　C. being invited D. having invited

　　解析:在条件状语从句中,如果从句主语与主句主语一致,且从句谓语部分含有be时,可将从句主语及be省略而只保留连词,从而构成省略。

　　真题回练

　　1. If ______ the same attention again, he is sure to get well.

　　A. giving B. give

　　C. given D. being given

　　2. The research is so designed that once ______ nothing can be done to change it.

　　A. begins B. having begun

　　C. beginning D. begun

　　Key:1-2 CD

　　五、考查分词表示条件概念的用法

　　典型题例

　　______more attention, the trees could have grown better.

　　A. Given B. To give C. Giving D. Having given

　　解析:该题考查过去分词表示条件概念的用法。Given...相当于If引导的条件句,表示一种假定。本句可译为:假如照管得好,树木会生长得更快。

　　特别提示:表示条件也可以用现在分词或独立主格结构。如:Supposing he is absent, what shall we do?假如他迟到了咋办?Other conditions being equal, the pressure remains constant.如果其他条件相等,压力会保持平衡。

　　真题回练

　　______in this light, the matter is not as serious as people generally suppose.

　　A. Seen B. To see C. Seeing D. Having seen

　　Key: A

　　六、考查暗含语境中条件概念的用法

　　典型题例

　　-There were already five people in the car but they managed to take me as well.

　　-It______a comfortable journey.

　　A. can't be B. shouldn't be

　　C. mustn't have been D. couldn't have been

　　解析:从语境there were...可知是对过去事情的表述,下文It...应是对过去情况的推测,要用"情态动词+have+过去分词",故D为正确答案。

　　真题回练

　　1. -We should have walked to the station, it was so near.

　　-Yes. A taxi______at all necessary.

　　A. wasn't B. hadn't been C. wouldn't be D. won't be

　　2. He______you more help, even though he was very busy.

　　A. might have given B. might give

　　C. will give D. may give

　　3. Yesterday, Jane walked away from the discussion, otherwise, she______something she would regret later.

　　A. had said B. said C. might say D. might have said

　　Key:1-3 AAD

　　七、考查倒装虚拟条件概念的用法

　　典型题例

　　What would have happened______, as far as the river bank?

　　A. Bob had walked farther

　　B. if Bob should walk farther

　　C. had Bob walked farther D. if Bob walked farther

　　解析:虚拟语气中采用从句倒装句式,把助动词、情态动词或be置于主语之前,这种形式就相当于if引导的条件状语从句。

　　真题回练

　　1. ______for the free tickets, I would not have gone to the film so often.

　　A. If it is not B. Were it not

　　C. Had it not been D. If they were not

　　2. ______it rain tomorrow, we would have to put off the visit to the Yangpu Bridge.

　　A. Were B. Should C. Had D. Will

　　Key: 1-2 CB

　　- "条件"表达法相关知识提示

　　1. with, without, on condition that等引导的结构或句子表示条件概念。

　　With your permission, we will start this work right now.只要你允许,我们马上就着手做这项工作。

　　You can borrow my umbrella on condition that you return it in time.只要你能按时归还这把雨伞,你可以借去用。

　　2. once充当连词引导从句,表示条件概念,意思是"一旦……(就)"。

　　Once you see him, you will never forget him.一旦你看见了他,就再也忘不了他了。

　　3. as long as或so long as引导从句表示条件概念,其意为"只要/如果……"。

　　They can go out as long as they promise to be back before eleven.如果他们答应能在十一点前返回就让他们出去吧。

　　4. but用作并列连词隐含条件概念

　　I should have come earlier, but I haven't enough time.如果我有足够的时间,我本该早点儿来。

　　5.动词不定式表示条件概念

　　A man would be blind not to see that.一个人如果连那点都看不清楚真是瞎得够可以的。

　　6.比较级形式表示条件概念

　　A less difficult problem would have already been solved.要是问题容易些早就解决了。

　　7. only if或if only引导从句表示条件概念

　　Only if you work hard, you will pass the exam.只要你努力,考试就会及格。

　　If only I had come, I would have met him.我要是来的话,本来会碰到他的。

　　8. but for / except for接名词或名词短语表示条件概念

　　But for air and water, nothing could live.没有空气和水,什么也活不了。

　　She would have left her husband except for the children.要不是为了孩子她那时可能就离开她丈夫了。

　　9.定语从句表示条件概念

　　Anyone who should do that would be laughed at.如果谁要是那样做只能让人笑话。

　　A country that stops carrying out reform and open-door policy would not develop fast.一个国家如果不坚持改革开放就得不到快速发展。

　　(文/梁建成；英语辅导报高三版2003-2004学年第35、36期；版权归英语辅导报社所有，独家网络合作伙伴新浪教育，未经许可，不得以任何形式进行转载。)