由一個主句和一個或一個以上的從句構成的句子叫復合句。名詞性從句在復合句中起名詞的作用，它包括主語從句、賓語從句、表語從句、同位語從句四大類，在句中分別用作主語、賓語、表語和同位語。

引導名詞性從句的關聯詞

A.that

連詞that本身沒有意義，在從句中不擔任任何句子成分，在賓語從句中有時可省略。

I hear (that) he has joined the football club. 我聽說他已經加入了足球俱樂部。

That light travels in straight line is known to all. 眾所周知，光是以直線傳播的。

It so happens that I know the man. 碰巧我認識那個。

Is it certain that they will win 他們一定會贏嗎

B.whether和if

連詞whether和if本身有意義(解釋是否)，在從句中不可省略。

1.whether可以連接所有的名詞性從句，而if只能引導賓語從句。

I didn't know whether he would attend the concert. 我并不知道他是否參加音樂會。(賓語從句，可用if代替whether)

The question is whether it s worth trying. 問題是值不值得試一試。(表語從句，不可用if代替whether)

Whether she comes or not makes no difference. 她來不來都沒有關系。(主語從句，不可用if代替whether)

He must answer the question whether he agrees to it or not. 他必須回答他是否同意此事這樣一個問題。(同位語從句，不可用if代替whether)

2.whether引導的賓語從句可作介的賓語，而if則不能。

It all depends on whether they will support us. 這完全取決于他們是否支持我們。(不用if)

Ryan was worrying about whether he had hurt her feelings. 瑞恩擔心是否傷害了她的感情。

3.if既可引導語從句，也可引導賓語從句。如果用if會引起歧義，應避免使用if，而用whether。

Please let me know if you want to join us. 請告訴我你是否想加入我們。(if引導的從句可被看成是賓語從句，if表示是否)

Please let me know if you want to join us. 如果你想加入我們的話，請告訴我一聲。(if引導的從句可被看成是條件狀語從句，if表示如果)

Please let me know whether you want t join us. 請告訴我你是否想加入我們。(為避免引起歧義，可用whether表示是否)

C.who, whom, whose, what, which

連接代詞who, whom, whose, what, which等在從句中既起連接作用，同時又擔當主語、賓語、定語、表語等成分。

No one knows who he was waiting for. 沒人知道他當時在等誰。

We are worrying about what we should do next. 我們正在為下一步該怎么辦而煩惱。

Tell me whos house it is. 告訴我這是誰的家。

Let me know which train you will be arriving on. 告訴我你將乘哪列火車到達。

D.where, when, how, why

連接副詞where, when, how, why等在從句中既是連接詞，又作狀語。

I don't know where we are going to have the meeting.我不知道我們將在哪兒開會。

She always thinks of how shecan work well. 她總是在想怎樣能把工作做好。

What I am anxious to know is when we can visit the museum. 我急于知道我們什么時候能參觀博物館。

比較：

when引導的時間狀語從句和名詞性從句中的不同時態(tài)。

Please lt me know when you arrive. 你到的時候，請告訴我一聲。(when引導的是時間狀語從句，從句中用一般現在時來表示將來。)

Please let me know when you will arrive. 請告訴我你什么時候到。(when引導的是賓語從句，從句中用一般將來時。)

E.whoever, whomever, whatever, whichever, whosever

連接代詞whoever = anyone who任何人, 無論誰;whatever =anything that凡是...，無論什么;whichever = anything that無論那一個, 任何一個;whomever = anyone whom (whoever的賓格形式)。

Whoever comes to the club is welcome. 不論誰來參加這個俱樂部都歡迎。

Whatever is worth doing at all is worth doing well.凡是值得做的就值得做好。

They ate whatever they could find o the deserted island. 他們在荒島找到什么就吃什么。

You may do whatever you will. 你可做任何你想做的事。

I'll take whichever book interests me.我愿買任何讓我感興趣的書。

Whosever book is overdue will be fined. 不管誰的書過期未還都要被罰款。

比較：

連接代詞whoever在賓語從句中作主語，whomever作賓語從句中賓語。

You may offer he book to whoever wants it. 你可把這本書給任何想要的人。(此句中不能使用whomever，因為whoever在賓語從句中作wants it的主語)

You may offer the book to whomever you like.你可把這本書給任何你喜歡的人。(whomever在賓語從句中作you like的賓語)

表語從句

表語從句放在連系動詞之后，充當復合句中的表語。

A.可接表語從句的連系動詞

可接表語從句的連系動詞有be, look, seem, sound, appear等。

China is no longer what she used to be. 今日的中國不再是過去的中國了。

The question remains whether they will be able to help us. 問題還是他們能否幫我們。

Itappears that he has a taste for music.看來他對音樂有一定的鑒賞力.

At that time, it seemed as if I couldn' t think of the right word anyhow. 當時，我似乎怎么也想不出一個恰當的字眼來。

B.as, as ifthough引導的表語從句

He looked just as he had looked ten years before. 他看起來還與十年前一樣。

It sounds as ifsomeone is knocking at the door. 聽起來好像有人在敲門。

C.because, why引導的表語從句

I think it is because you are talking too much. 我想這是因為你話說得太多。

That's because he didn't understand me. 那是因為他沒有理解我。(That's because

同位語從句

同位語從句用于對前面的名詞作進一步解釋，說明名詞的具體內容。同位語從句一般由that引導，但也可以由whether 以及連接代詞和連接副詞引導。

A.同位語從句一般跟在名詞fact, hope, idea, news, doubt, suggestion, information, opinion, decision, discovery, truth, promise, statement, problem, rule等的面。

They were all very much worried over the fact that you were sick. 對你生病這件事，他們都很焦慮。

Where did you get the idea that I could not come 你在哪兒聽說我不能來?

I have no idea whether he'll come or not. 我不知道他是否來。

We haven't yet settled the question where we are going t spend our summer vacation. 到哪兒去度暑假，這個問題我們還沒有決定。

It is a question how he did it. 那是一個他如何做了此事的問題。

There is no doubt that we will win. 毫無疑問我們會贏的。

注意：

當含有同位語從句的主句謂語部分過短時，可以把謂語動詞提前，使同位語從句與名詞隔開，以避免頭重腳輕的現象。

Word came that Mr President would come and inspect ourschool himself. 有消息說總統先生將親自來視察我們學校。

B.使用虛擬語氣的同位語從句

在一些表示建議、命令、要求的名詞后的同位語從句中，謂語動詞用should+動詞原形表示，should可省略。

This is our only request that this (hould) be settled as soon as possible. 盡快解決這個問題，這是我們唯一的請求。

He made the suggestion that we go by train. 他建議我們坐火車去。

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