4.whether 和 if 都可引导宾语从句，但 whether后可紧跟or not；whether从句可作介词的宾语。
例句：The headmaster hopes everything goes well.
例句：She was sorry that she hadn’t finished her work on time.
例句：The teacher told his class that light travels faster than sound.
False: He is wondering when can he finish this difficult job.
Right: He is wondering when he can finish this difficult job.
B. 有时候可以用it 作形式宾语，而把真正的宾语从句放在后面。
Bad: I thought that he could finish this job in just two hours impossible.
Good: I thought it impossible that he could finish this job in just two hours.
Bad: I think he doesn’t like the English teacher.
Good: I don’t think he likes the English teacher.
False: He wanted to know why he is crying in the corner.
Right: He wanted to know why he was crying in the corner
I don’t think he will come to my party.而不能说成I think he won’t come to my party.
I don’t believe that man is killed by Jim,is he?
We find that he never listens to the teacher carefully,does he?
连词：that (that 常可省略),whether, if
代词：who, whose, what ,which
副词：when ,where, how, why 等。
say, think, insist, wish, hope, demand, imagine, wonder, know, suppose, see, believe, agree, admit, deny, expect, explain, order, command, feel, dream, suggest, hear, mean, notice, prefer, request, require, propose, declare, report等。
例句：The boy believes that he will travel through space to other planets.
注意事项：当主句谓语动词是 think, believe, suppose, expect 等词，而宾语从句的意思是否定时，常把否定转移至主句表示。
例句：I don’t think it is right for him to treat you like that.
例句：He said (that) you were too young to understand the matter and that he was asked not to tell you.
例句：Just then I noticed, for the first time, that our master was wearing his fine green coat and his black silk cap.
例句：I can’t tell him that his mother died.
例句：I find it necessary that we should do the homework on time.
例句：I wonder whether(if) they will come to our party.
例句：We decided whether to walk there.
例句：I’m thinking of whether we should go to see the film.
例句：We discussed whether we had a sports meeting next week
例句：I can’t say whether or not thet can come on time.
例句：The students will go on a picnic if it is sunny.
例句：He asked if I didn’t come to school yesterday.
c.引导状语从句even if（即使）和as if（好象）时
例句：He talks as if he has known all about it.
c. whether后可以加or not,但是if不可以.
（如：I can’t decide whether to stay. 我不能决定是否留下。）
用于这种结构的动词常常是：see, say, tell, ask, answer, know, decide, show, find out, imagine, suggest, doubt, wonder, discover, understand, inform, advise等。
例句：Can you tell me whom you are waiting for?
例句：None of us knows where these new parts can be bought.
当主句谓语动词是hope， decide， wish， choose， agree， promise等，
Li Ming hopes he will be back very soon.
→Li Ming hopes to be back very soon.
We decided that we would help him.
→We decided to help him.
方法二：当主句谓语动词是know， learn， remember， forget， tell等动词，
She has forgotten how she can open the window.
→She has forgotten how to open the window.
注：当主句谓语动词是tell， ask， show， teach等动词，
Could you tell me how I can get to the station？
→Could you tell me how to get to the station？
The headmaster ordered that we should start at once.
→ The headmaster ordered us to start at once.
He insisted that he should go with us.
→He insisted on going with us.
The poor boy doesn’t know when and where he was born.
→The poor boy doesn’t know the time and the place of his birth.
Liu Ping found that there was a wallet lying on the ground.
→ Liu Ping found a wallet lying on the ground.
It seemed that the boys were going to win.
→The boys seemed to win.
I found that it was difficult to learn English well.
→I found it difficult to learn English well.
Soon we found that the ground was covered with thick snow.
→Soon we found the ground covered with thick snow.
They found that the box was very heavy.
→They found the box very heavy