(1)在主语从句中用来表示惊奇、惋惜、理应如此等，其谓语形式是"should(可省) +动词原形"，常用于以下三种句型中。
句型一：It is necessary (important, natural, strange, etc) that…
句型二：It is a pity (a shame, no wonder, etc) that…
句型三：It is suggested (requested, proposed, desired, etc) that…
如：It is strange that he (should) have done that.
It is a pity that he (should) be so careless.
It is requested that we (should) be so careless.
(2)在宾语从句中用于suggest, propose, move, insist, desire, demand, request, order, command等动词后的宾语从句中，表间接的命令和建议。其谓语形式是"(should)+动词原形"。如：I suggest that we (should) go swimming.
(3)在表语从句中，表示间接的命令，要求、请求、建议、决定等，主句中的主语通常是suggestion, proposal,request, orders, idea等。从句谓语形式是"(should)+动词原形"。如：
His suggestion is that we (should) leave at once.
(4)在同位语从句中，谓语形式是"(should)+动词原形"。如：We received order that the work be done at once.
(5)在It is time that…句型中，其谓语动词形式是"动词的过去式"或"should +动词原形",should不可省。如：It's time that we went ( should )go to school.
(1)主语从句
What he wants is a piece of paper.
It is believed that he can solve the problem.
(2)宾语从句
I don't know how to solve the problem.
Do you know where he lives?
(3)表语从句
The problem is who can help me.
(4)同位语从句
I have no idea where he went.
I heard the news that he would come.
同位语从句用that引导，常跟在fact, idea, news, promise, thought, message, hope, belief, doubt等词后，that在从句中不作任何成分。
2、定语从句
在复合句中，修饰某一名词或代词，或修饰整个主句的从句叫做定语从句，引导定语从句的关系代词有who, whom,whose, which, that, as,和关系副词when, where, why。
(1)that指物时一般可与which互换，但在下列情况下，要用that而不用which。
a.先行词有all, everything等不定代词时，如，Everything (that) he did is wrong.
b.先行词被all, every, no, some, any, little, much等修饰时，如，I'll read all the books (that) you lend me.
c.先行词被序数词或形容词最高级修饰时，This is the first letter (that) the boy has written.
d.先行词被the only, the very, the same, the last修饰时，如He is the very man (that) I'm looking for.
e.只用which的情况在介词后或在非限定性定语从句中
This is the book about which we have talked a lot.
The book, which he gave me yesterday, is very interesting.
f.where和when作关系副词
This is the room where I worked.
This is the room which I stayed in.
I remembered the day when we lived there.
I remembered the day that I spent there.
g.as和which
As you know, he is good at English.
three of them 和three of which
I have a lot of books, three of which are in Russian.
I have a lot of books and three of them are in Russian.
3、状语从句
在复合句中起状语作用的从句叫做状语从句。状语从句可分为时间状语、地点状语、原因状语、目的状语、结果状语、条件状语、行为方式状语、比较状语、让步状语等多种。
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