1.whether和if均可用来引导主语从句，但if引导的从句不能位于句首。
如： Whether they win or lose is all the same to me.  他们是赢是输於我都一样.（此时whether不能换作if ）
    It's doubtful whether there'll be any seats left.    说不上还有没有空座位了. (此句whether能换作if)

2.whether和if均可用来引导宾语从句。
如：①I don't know whether/if I will be able to come.我不知道我是否能来.
②She asked me whether/if I was interested in working for her.她问我是否有兴趣为她工作。
③We'll be told tomorrow whether we should take the exam or not.我们明天才知道是不是应该参加考试.
 ④I asked him whether he had done all the work himself or whether he had had any assistance. 我问他这些工作都是他自己做的还是别人帮他做的.
( 注意: 在两个供选择的从句之间若用or字, 则须重复whether一字. )


注:  ⑴当强调宾语从句并将其提前时只能用whether。
    如:Whether I'll have time to go with you I am not sure.我很难说我们是否有时间跟你们一起去。
      ⑵ 从句作介词宾语时只用whether不用if。
如:She was undecided about whether she should accept his offer.她拿不定主意应该不应该接受他的好意
      ⑶ 当whether和or not连用时，只用whether不用if。当or not放在whether引导的从句句尾，则可以        用if来替换。
      如: I don’t know whether or not he will come.我不知道他是不是回来。
      I'll be happy whether/if I get the job or not我能不能得到那份工作都一样高兴
      ⑷ 当whether和or 连用表示明确的选择时，只用whether不用if。
      如:He asked me whether I wanted to go there by train or by bus.他问我是想乘火车还是坐公共汽车去那里。
          He hesitated about whether he should drive or take the train.他开车去还是坐火车去,
犹豫不决

注:whether 和or 连用还可以引导让步状语从句,此时也不用if。
    如：We'll go on with the work, whether we can find the necessary tools or not.
不管我们能否到所需的工具,我们要把这件工作做下去。
            Whether or not it rains / Whether it rains or not, we're playing football on Saturday.
              无论下不下雨, 我们星期六一定踢足球.
    ⑸ 动词discuss，decide,consider等后习惯上也常用Whether引导从句，不用if。
        They discussed whether they should leave at once.他们讨论了是否应该马上离开。 
      We discussed whether the house should be sold.  我们讨论了这房子是否应卖掉。   
whether是什么意思

3.表语从句用whether引导不用if.
如:①The doubt was whether you had broken the beautiful vase.      疑问是你是否打坏了这只漂亮的花瓶。

4. 同位语从句用whether引导不用if.
如:①The question whether we'll build another lecture building hasn't been settled.
是否要另建一幢教学楼的问题还未决定。
5. 在动词不定式之前，只能用whether，不能用if。
如:①The question is whether to go to Munich or Vienna.      问题是去慕尼黑还是去维也纳.
  ②She doesn't knows whether to get married now or wait.  是否现在结婚或是等待她不知道。
  ③We were wondering whether to go today or tomorrow.    我们弄不清是今天走还是明天走.
  ④I'm not sure whether to resign or stay on.              我拿不准主意是辞职还是留任.
强化练习：
1. The question has not been answered ____ Taiwan will be included on the Olympic torch relay route.
A．that      B．whether      C．which        D．if
2. You have not yet answered my question _____ I can join in the party tonight or not.   
  A. whether                B. if                              C. that                        D. which
3．— I d like to invite you to a party this evening.
— Thank you, but _____ I’ll be free I m not sure at the moment.
A. while                  B. if                      C. when        D. whether
4．---What are you anxious about?
    ---___________
A.      If we succeed  B.That we can succeed      C. Do we succeed  D.Whether we can succeed
5. Only when _____ the painting _____ decide ______the painting is worth buying.   
A. he sees, he can ,whether    B. does he see, can he,  if 
C. he sees, can he ,whether    D. sees he, he can,that
6. _____ English is his favourite subject
    A. I asked him if    B. I asked him that whether C. I asked him that    D. I asked him which
7. _____ they’ll go to the Summer Palace ____ the weather.
    A. If; depends on    B. Whether; depends upon  C. Whether; depended on    D. If; depended upon
8.It isn’t quite _____ ______ he will be present at the meeting.
    A. sure; whether    B. sure; if      C. certain; whether    D. certain; that
9. _____ the 2008 Olympic will be held in Beijing is not known yet.
    A. Whether    B. If    C. Whenever    D. That
10. No one was sure _____ he would be asked to speak next year.
    A. when    B. whether    C. what    D. how
11. It is still a question to us all _____ there is any living thing in some other places in the space.
    A. whether    B. which      C. what    D. where
12. I doubt _____ he will come here on time.
A. that    B. whether      C. when    D. where
13.    The point is not who said the words, _____ they are true or not.
A. but whether    B. and whether    C. but how    D. and how 
14. “What did he ask you?” “_____ I would be late.”
A. That    B. When    C. Where    D. Whether
15. He treated all the people around him,______he knew or he didn't know,______.
    A. if, friendly                B. whether, friendly
    C. if, in a friendly way      D. whether, in a friendly way
16. At the meeting, we discussed _____ we should employ more workers.
    A. if      B. whether    C. that    D.不填 



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