She wondered if/whether the buses would still be running.
介词后只能用whether，而不能用if。
如：She is not certain about whether she has done anything wrong.
当从句做主语放在句子开头时，只能用whether，而不能用if。
如：Whether it is going to clear up keeps me wondering.
只能用whether or not，而不能用if or not。
如：I want to know whether or not the train goes to King Street.
如果and或but引导两个并列的that或whether/if引导的名词性从句，后一个句子的that或whether/if不可省。
如：He said that he liked rain very much and that he wouldn t use an umbrella when it was raining.
No one knows whether it will be fine tomorrow and whether he will come to work.
第二单元
一 名词性从句：由疑问词引导的名词性从句
我们用以下的疑问词来引导名词性从句：what, which, who/whom, whose, when, where, why and how。
当从句是wh-引导的疑问句时，我们用疑问词来引导名词性从句。从句可以做句子的主语，宾语或表语。
如：Where a person comes from will affect their style of speech.
You can begin to see why English has such strange rules.
That is why English is a language with so many confusing rules.
我们把疑问词后面的句式改成陈述句的语序。
如：What are people from the north saying? People from the south find it difficult to understand.
People from the south find it difficult to understand what people from the north are saying.
3．在任何情况下，都不可以省略名词性从句中的疑问引导词。
二 形式主语it
在英语中，我们通常把最重要的信息放在句子的末尾用于强调。这被称做句末强调效果。用形式主语it就可以达到这一效果。It只是语法意义上的主语，真正的主语在句子的后面。 我们通常用it来做形式主语。
当我们用一个名词性从句来做句子的主语时：
（更好的）It is certain that we would not be able to understand Old English today. （正确的）That we would not be able to understand Old English today is certain.
当主语是带to的动词不定式时：
（更好的）It is hard to master a foreign language.
（正确的）To master a foreign language is hard.
当主语是动词-ing形式时：
（更好的）Smoking is difficult to stop.
（正确的）It is difficult to stop smoking.
It可以被放在seem，appear，happen，chance，turn out 和prove前做句子的形式主语。 如：It seems that he speaks two languages.=he seems to speak two languages.
