很高想为你作答：
在句子中起名词作用的句子叫名词性从句 (Noun Clauses）.名词性从句的功能相当于名词词组,它在复合句中能担任主语、宾语、表语、同位语、介词宾语等,因此根据它在句中不同的语法功能,名词性从句又可分别称为主语从句、宾语从句、表语从句和同位语从句.
作句子主语的从句叫主语从句.
主语从句通常由从属连词that,whether,if和连接代词what,who,which,whatever,whoever以及连接副词how,when,where,why等词引导.that在句中无词义,只起连接作用；连接代词和连接副词在句中既保留自己的疑问含义、又起连接作用,在从句中充当从句的成分.
例如：What he wants to tell us is not clear.他要跟我们说什么,还不清楚.
Who will win the match is still unknown.谁能赢得这场比赛还不得而知.
It is known to us how he became a writer.我们都知道他是如何成为一名作家的.
Where the English evening will be held has not yet been announced.英语晚会将在哪里举行,还没有宣布.
名词从句用作宾语的从句叫宾语从句.引导宾语从句的关联词与引导主语从句表语从句的关联词大致一样,在句中可以作谓语动词或介词及非谓语动词的宾语.
如 He has told me that he will go to Shanghai tomorrow.他已经告诉我他明天要去上海.
I want to know what he has told you.我想知道他告诉了你什么
在句中作表语的从句叫表语从句.引导表语从句的关联词与引导主语从句的关联词大致一样,表语从句位于连系动词后,有时用as if引导.其基本结构为：主语 + 系动词 + that从句.
例如：The fact is that we have lost the game.事实是我们已经输了这场比赛.
That’s just what I want.这正是我想要的.
This is where our problem lies.这就是我们的问题所在.
同位语从句说明其前面的名词的具体内容.
同位语从句通常由that引导,可用于同位语从句的名词有advice、demand、doubt、fact、hope、idea、information、message、news、order、problem、promise、question、request、suggestion、truth、wish、word等.
例如：The news that we won the game is exciting.我们赢得这场比赛的消息令人激动.
I have no idea when he will come back home.我不知道他什么时候回来.
The thought came to him that Mary had probably fallen ill.他想到可能玛丽生病了.
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