从句在句中可用作主语、表语、宾语、定语、状语等句子成分;

　　a)主语从句(subject clause)如What I want to say is this(我要说的是这么一点)中的what I want to say。

　　b)表语从句(predicative clause)如This is what I want to say(这是我要说的)中的what I want to say。

　　c)宾语从句(object clause)如I have said what I want to say(我说完了我要说的话)中的what I want to say。

　　d)定语从句(attributive clause)如This is the thing I want to say(这就是我要说的)中的I want to say。

　　e)状语从句(adverbial clause)如If you want to say something，say it clearly(假如你要说什么，就应说清楚)中的if you want to say something。

　　句子(sentence)内含主语部分和谓语部分，有比较完整的意义的一组词，叫做句子。