1.主语从句
1）主语从句可直接位于主语的位置，如果从句较长，谓语又较短，可用it 作形式主语，而将从句放在句末。常见的句型有：
It is a fact\ a pity\ a question\ good news that...
It seems\ appears\ happened\ has turned out that...
It is clear\ important\ likely\ possible that...
It is said\ reported\ estimated\ has been proved that...
如：It is said that comic books create a connection between people of the same generation.
It seems that the performance is very useful.
2）what 引导的主语从句表示“...的东西时”，一般不用it 作形式主语。
What we lack is experience.
3）what, who, when, why, whether 等词含有各自的疑问意义，但它们引导的主语从句，都用陈述语序。
How the plan is to be carried out should be discussed again.
I did know why I felt like crying.
2.宾语从句
1）宾语从句可位于及物动词、介词和某些形容词后。连词that 常可省略。介词后一般接疑问词引导的宾语从句。
in that (因为)，except that (除了)，but that (只是）已构成固定搭配，其他介词后一般不接that 引导的宾语从句。
如：I promised that I would change the situation.
All this is different from what American young people would say about friendship.
He is certain that watching so much television is not good for children.
This article is well-written except that it is a bit too long.
2）宾语从句后如有宾补，要用形式宾语it 来代替，而把宾语从句移至宾补之后。
He has made it clear that he would not change his mind.
3）在think, believe, suppose, expect等动词后的宾语从句中，如果谓语是否定的，一般将否定词移至主句谓语上，宾语从句则变成肯定形式。
He didn't think that the money was well spent.
3.表语从句
表语从句出现在结构为“主语+系动词+表语从句”的句子中。表语从句除可用
that, what, when, why, whether, how等引导外，还可由because, as if (though) 等引导，that 常可省略。
如主句主语为reason ，只能用that 引导表语从句，不可用because 。
Perhaps the most important thing to remember is that there is no one common type of life in America.
The reason why so many people died there is that there were not enough food supplies.
It looks as if successful international cultural communication will make the world smaller.
4.同位语从句
同位语从句用于对前面出现的名词作进一步说明，一般用连词that 引导，由于先行名词的意义不同，也可用whether, who, when, where, what, why, how 等引导。
常见的先行名词有fact, idea, belief, news, hope, conclusion, evidence, suggestion, order, problem, report, decision.
有时由于谓语较短，将同位语从句位于谓语之后。
如：She finally made the decision that she would join the fashion show.
I had no idea how many books I could borrow at a time.
The news came that their team had won the championship.
