名词性从句(Noun Clauses)
在句子中起名词作用的句子叫名词性从句。名词性从句的功能相当于名词词组，它能在复合句中作主语、宾语、表语、同位语等。根据它在句中不同的语法功能，名词性从句分为主语从句、宾语从句、表语从句和同位语从句。在名词性从句中，连接词that既没有实际意义，又不充当任何成分，只起引导从句的作用， 引导宾语从句时经常省去。
一、主语从句 (The Subject Clause)：在复合句中作主句的主语。为保持句子结构平衡，主语从句通常被置于句末，而用it作形式主语。
That light travels in straight line is known to all.
When the plane is to take off hasn’t been announced.
It was my fault that I had him play football yesterday afternoon.
It is important that we should go to the school to talk with the teacher.
It is still unknown which team will win the match.
二、宾语从句 (The Object Clause)：主要作及物动词的宾语，有时置于介词或形容词之后。
He said (that) his father had come back from the United States.
He asked how much I paid for the violin.
No one can be sure what man will look like in a million years.
如果宾语从句带有补足语，通常用it作形式宾语，而把宾语从句置于补足语之后。
I think it necessary that we should pay close attention to SARS.
We all feel it our duty that we should serve the people heart and soul.