“whether”与“if”都可表“是否”，是常考内容。下面的顺口溜可帮你记住其异同。

主从表从同位从，if 不用 whether 用；

discuss 和介词后，whether 引宾从；

不定式、or not 后面跟，whether 独能显神通；

宾从如是否定句，if 发挥其功用；

避免歧义要慎重，其它情况可换用。

1．Whether we'll go camping depends on the wheather．( 这里指句首主语从句 )

2．The question is whether it is worth doing．

3．The question whether we need it has not been decided．

4．We should discuss whether we shall hold the meeting．

5．I'm worried about whether he call arrive in time．

6．I don't know whether to stay or not．

7．Please tell me whether or not you agree．

8．I don't care if you won't come．

9．I'll tell you whether he is busy． ( 若将句中“whether”改成“if”，则有歧义，因“if”还有“如果”之意。 )

10．I don't know whether (if) he will succeed．

11．It is uncertain whether he is coming．

12．Can you tell me whether the train has left or not？

Exercise：

用 whether 或 if 填空。

1．Ask him ____ he can come．

2．I wonder ____ it is the right answer．

3．She doesn't know ____ to go the cinema or watch TV．

4．I want to know ____ or not he is well．

5．____theOlympicGameswillbeheldinBeijingin2008hasn'tbeen decided yet．

6．—When will the sports meet be held？—It depends on ____ it rains the day after tomorrow．

Key：1．whether ／ if 2．whether ／ if 3．whether4．whether 5．Whether 6．whether