英語的語法中，復合句有三大類型：定語從句，狀語從句和名詞性從句由于名詞性從句中的賓語從句 在之前討論過，本文討論剩下的主語從句，表語從句和同位語從句。
主語從句
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從句在句子中做主語。
引導詞通常是連詞that,whether,who,what,whatever等
通常按第三人稱單數對待
That
句子成分完整的時候，用that引導。
從句和主句的變化可以組合出不同的句子。
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That you don\’t know the rule is not an excuse for your failure. 你不知道規則并不能成為你失敗的理由。
That real estate price will go down is certain. 房地產價格下降將是必然。
Whether
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Whether she will get married or not is still unknown
who whoever whom whose what whatever which whichever
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Who will win the match is still unknown.
What he wants to tell us is not clear.
Whatever you do is not my primary concern. 你做任何事都不是我們首要關心的
when where how why
When will he get married remains unknown.
Why you are so clever is a puzzle we all want to work out
It作形式主語
It be 形容詞 that從句
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It is certain that real estate price will go down
It is true that she will get married in winter.
It be 名詞詞組 that從句
no wonder, a pity, a honour, no surprise
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It is a pity that you will married him, not me. 很可惜，你要嫁的是他不是我。
It is an honor that you come to our little party.
It be 過去分詞 that從句
said，believed，announced, expected
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It is said that she has been pregnant for 3 months. 據說她已經懷孕三個月。
It is believed that success comes from hard work.
It doesn\’t matter (makes no different) 連接代詞或副詞引導的主語從句
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It doesn\’t matter when he will arrive.
It makes no difference whether he will come to the part or not.
表語從句
如果不懂表語是什么，請先復習
從句在主系表結構的主句中充當表語成分
常用連接詞：that, what, who, when, where, which, why, whether, how, whoever，whichever ，whatever
reason 用that引導
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The reason why he was late was that he missed the train by one minute this morning.
The fact is that we have lost the game.
可用be，look，seem, sound, appear引導
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It looks as if it is going to rain.
whether可引導表語從句，但與之同義的if卻通常不用于引導表語從句。
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We know things will turn out to be better. The question is whether we can survive to see that day. 我們都知道形勢終將變好，問題是我們能不能或者看到那天。
That is because …指原因或理由。
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He did not drink with us last night. That is because he had to help his little sister with her homework.
That is why … 指由于各種原因所造成的后果。
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He was married. That is why he refused your proposal.
同位語從句
從句充當同位語成分，起解釋說明作用
被解釋說明的詞和同位語在邏輯上是主語和表語關系
主語you和同位語the elder brother就是主謂關系：you are the elder brother. 同位語elder brother是對you的解釋。
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You, the elder brother, should take care of your sister.
The question who can do the work requires consideration.
You must answer the question whether he agrees with the plan or not.
區分定語從句同位語從句
主語和同位語是主表關系，主從句間加is說得通就是同位語，不通是定語.
The news that he told me yesterday is true.
上句是定語從句， he told me是用來限定the news的。
That fact that you are late surpised everyone. You have never been late before. 你遲到的事實驚呆了所有人。以前從來不遲到。
The fact is you are late,說的通，所以是同位語。
