(1)It+be+名词+that从句 (2)It+be+形容词+that从句 (3)It+be+动词的过去分词+that从句 (4)It+不及物动词+that从句
注意：主语从句中用来表示惊奇、不相信、惋惜、理应如此等语气时，谓语动词要用虚拟语气“should+do”，常用的句型有： (1) It is necessary(important,natural,strange,etc)that… (2) It’s a pity(a shame,no wonder,etc)that…
(3) It is suggested(required,proposed,desired,etc)that…
5、wh-疑问词引导的主语从句，可以放在句首(1)，也可以借助形式主语it(2)。 (1)When he’ll be back depends much on the weather. How it was done was a mystery.
Whether we’ll succeed remains to be seen. (2)It is uncertain whether the game will be held. It’s a puzzle now life began. It doesn’t matter much where we live. Is it known where he went?
（二）定语从句
一、1、定义：修饰一个名词或代词的从句称为定语从句，一般紧跟在所修饰的先行词后面。
2、关系词：引导定语从句的关联词称为关系词。
关系词有关系代词和关系副词。关系代词有that,which,who,whom,whose,as等； 关系副词有where,when,why等。
关系词常有3个作用：（1）引导定语从句，（2）代替先行词，（3）在定语从句中担当一个成分。
二、关系代词引导的定语从句： 1、who指人，在从句中作主语。
(1)The boys who are playing football are from Class One. (2)Yersterday I helped an old man who lost his way. 2、whom指人，在定语从句中充当宾语，常可省略。 (1)Mr. Liu is the person whom you talked about on the bus. (2)Mr. Ling is just the boy whom I want to see.
注意：关系代词whom在口语和非正式语体中常用who代替，可省略。 (3)The man who/whom you met just now is my friend. 3、which指物，在定语从句中作主语或者宾语，作宾语时可省略。 (1)Football is a game which is liked by most boys. (2)This is the pen which he bought yersterday. 4、that指人时相当于who或者whom；指物时，相当于which。在宾语从句中作主语或者宾语，作宾语时可省略。
(1)The number of the people that/who come to visit the city each year rises one million.
(2)Where is the man that/whom I saw this morning?