⑥whether与if用法之异同：
1）whether 和if都可用来引导宾语从句，尤其是主要谓语动词为：see，ask，learn，tell，know，wonder，doubt，find out等时。
Go and see whether / if he can come.
I asked him whether /if he knew her.
We doubt whether / if it is true.
2）当宾语从句前置时，用whether而不用if来引导。
Whether it is true or not, I can′t say.
3）尽管二者都可引导宾语从句，但在表示一个选择概念时，用whether而不用if。
He wondered whether he should wait or go on.
4）尽管二者都可引导宾语从句，但如果用if代替whether会产生意义分歧时，两者不可换用。试比较：
Let us know whether she is coming. 告诉我们她是否要来。
Let us know if she is coming. 告诉我们她是否要来。/ 如果她要来，请告诉我们。
5）在多重复句中，如果句中本身已有一个if引导的条件从句，为避免重复，最好改用whether。
Bill asked whether, if I got the job, I would move to New York.
6）引导主语从句，表语从句，同位语从句时用whether；引导条件状语从句时用if。
Whether he comes or not has nothing to do with us.
It matters little whether / if we will go or not.（主语从句后移时，可用if来引导。）
The question whether we should have another meeting must be decided.
The question is whether we can get there in time.
We will not go there if it rains tomorrow.
7）whether 之后可以直接跟or not，而if 则不能。
We didn′t know whether / if he was ready or not.
I don′t care whether or not（不能说if or not）your car breaks down.
8）名词之后只能用whether（即whether能引导一个同位语从句）。
The question whether he should come himself or not must be decided.
9）介词之后只能用whether；动词不定式之前只能用whether（构成“疑问词 + 不定式结构”）。
I haven’t settled the question of whether I’ll lend him the money.
It depends on whether he will come.
She has not decided whether to go or not.
10）whether经常与or连用引导一个让步状语从句，意为“无论……还是……”。
Whether he drives or takes the train, he should be here on time.
Whether we go or whether we stay, the result is the same.
常可使用简略说法：
We will take the next offer, whether good or bad.
Almost all can enjoy, whether boys or girls, men or women, young or old.
⑦一般来说，若宾语从句之后还带有宾补时，这个宾语从句需要后移，在其原来位置上使用形式宾语it。动词love，like，dislike，hate，appreciate，see to，take … for granted（这类动词很少在后面直接带that引导的宾语从句）等后带宾语从句时，先使用it作为媒介，然后再带上that引导的宾语从句。
They make it clear to the public that the government has decided to take measures to prevent all the rivers and lakes from being polluted.
We think it important that all the citizens should get well educated.
I hate it (that) you speak to others with your mouth full.
We like it (that) you help others out when they are in trouble.
I would appreciate it if you call back this afternoon for the doctor’s appointment.
He took it for granted that we had arrived and finished the work ahead of time.
She’ll see to it (that) he goes ahead. （see to it that-clause 意为：“负责做到，设法做到，注意做到”）
⑧直接引语和间接引语
直接引述别人的话，引述内容加有双引号，叫“直接引语”；转述别人的话，叫“间接引语”。间接引语在很大程度上就是一个宾语从句。例如：
John said,“I like reading adventure stories.”（direct speech）
John said (that) he liked reading adventure stories.（indirect speech）
A.句型的转变
ask sb.(not) to do (…) tell sb.(not) to do (…)
order sb. (not) to do (…) warn sb. (not) to do (…)
want sb.(not) to do (…) advise sb. (not) to do (…)等等。
1. He said,“I have been to Beijing twice.”
→He said (that) he had been to Beijing twice.
2. Tom said,“Our team is to win the game.”
→Tom said (that) their team was to win the game.
3. He says,“I am the hardest student in the class.”
→He says(that) he is the hardest student in the class.
4. He asks,“ Does my little brother study hard ? ”
→He asks whether / if his little brother studies hard.
5. He asked,“ Are you a student? ”
→He asked if I was a student.
6. He said,“ Where has Tom gone? ”
→He asked where Tom had gone.
7. He said to me,“ What are you doing? ”
→He asked me what I was doing.
8. “ Make sure the door is shut,”she said to her little son.
→She told her little son to make sure the door was shut.
9. “ Don′t smoke in the room,”he said to me.
→He warned me not to smoke in the room.
10. “Do be careful,” he said to us.
→He asked us to be careful.
B.人称和时态的转变
一般来讲，间接引语中的人称变化要与主句中的主语保持人称和数的呼应与一致。例如：
1.“We run this restaurant to make friends,” says the manager,Hu Ming.
→Hu Ming, the manager, says(that)they run that restaurant to make friends.
2. “ We are unhappy about this,” said the students′parents.
→The students′parents said that they were unhappy about that.
3. “ The teacher has already told me that I should spend more time on study,” says John.
→John says that the teacher has already told him that he should spend more time on study.
4. “ We don′t have the money to hire enough waiters or waitresses, so we do most of the work ourselves ,” says Ms.Green.
→Ms. Green says that they don′t have the money to hire enough waiters or waitresses, so they do most of the work themselves.
5. “ I will never forget this interesting lesson,” said Paul.
→Paul said(that)he would never forget that interesting lesson.
6. “ We like skiing,” Steve said to Joe.
→Steve told Joe that they liked skiing.