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.
不管我们能否找到所需的工具,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。
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
Answers: BADDC ABCAB ABADD B
