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各种从句的语法总结
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虚拟语气在各种从句的应用
主语从句的虚拟
1. It is + adj. + that sb. (should) do
常见的形容词有：necessary, important, strange, natural
It's important that he take my advice.
2. It is + n. + that sb. (should) do
常见的名词有：a pity, a shame, no wonder, one's wish
It's a pity that he be so silly.
3. It is + done + that sb. (should) do
常见的过去分词有：suggested, advised, demanded, requested, required, asked, ordered,
proposed, decided, desired, insisted等。
It's requested that she go home as soon as possible.
宾语从句的虚拟
1. 表命令，表建议，表要求的动词，后接宾语从句虚拟。虚拟的构成为(should) do。
I advise that he stay at home.
2. wish后接从句，虚拟的构成是往过去推一个时态。
I wish I had watched the football match last night.
注意以下几组词或短语用于虚拟语气中。
1. as if, as though
He speaks English as if he were a native speaker.
2. otherwise, but, even though
He was ill. Otherwise he would have been there.
3. with, without, but for
Without your help, I would have died two years ago.
But for your help, I would have died two years ago.
4. would rather I'd rather you told me yourself.
5. It's time that
It's time that you went to bed.
It's time that you should go to bed.
表语从句中的虚拟
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.
名词从句部分：
1. that不可省略的情况
2. that引导同位语从句和that引导定语从句的区别：同位语从句中的that是连词，不做成分，只连接主从句，不能省略;定语从句中的that要代替先行词在从句中做主语、宾语或者表语，并且做宾语时可以省略。从语义上看，同位语从句是对前面名词的解释、说明或内容;而定语从句时对前面名词的限定。
We should consider the students’request that the school library provide more books on
popular science. (that引导同位语从句)
The only hope that he expressed was that they would do what they could to help the people
in disaster areas. (that引导定语从句)
3. 要根据句子结构尤其是谓语动词判断从句的类型：
What is known to us all is that the 2008 Olympic Games took place in Beijing.
本句含有一个主语从句和一个表语从句，主句的动词为is。
It is known to us all that the 2008 Olympic Games took place in Beijing.
本句含有一个主语从句，主句的动词为is known to。
As is known to us all, the 2008 Olympic Games took place in Beijing.
本句含有一个定语从句，主句的动词为took place，as引导非限制性定语从句。
4. 名词性从句的语序和语态。
名词性从句均应用陈述语序，不能用疑问语序，其时态应该和主句时态保持一致。
5. 名词性从句中连词的省略。
介词后的连词以及引导主语从句和同位语从句的连词不可省略。that引导名词从句(除了引导第一个宾语从句可省略外)都不可省略，但是引导定语从句并在从句中做宾语时可以省略。 that不能省略的情况：1)介词后面的that不能省略：
Peter is a good student except that he is sometimes careless.
2)当that引导的宾语从句位于句首时：
That he ever did such a thing I don’t believe.
3)主句谓语动词和that从句之间有插入语，that不省略：
She said that, if she failed, she would try again.
4)当宾语从句有其他从属连词时，that不省略：
He told me that if it was necessary they would work extra time.
6.名词性从句中it的使用：
为了保持句子平衡，多数情况下，it作形式主语或形式宾语，将真正的主语或宾语从句后置。 定语从句关系代词有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 可以放于句首，而which 不可以
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.
(2. )“介词+关系代词”的情况：
在固定短语中介词不能提前;判断介词的口诀：瞻前顾后看意义
瞻前——看先行词;顾后——找从句动词;看意义——看全句表达含义
(3. )先行词在从句中充当地点状语时，关系词用where 或者介词加which;先行词在从句中充当时间状语时，关系词用when或者介词加which;先行词在从句中充当原因状语时，关系词用why或者for which。
(4. )注意as和which在非限制性定语从句中代表主句所表达的内容的区别：
位置不同：as从句放在主句前或后均可;而which从句只能放在主句后
作用不同：as从句动词常常是see \know等，因而相当于插入语;which从句则在陈述一件事实。
状语从句部分
1.while 是高考中的高频词，它既可引导时间状语从句，又可引导并列句，还可引导让步状语从句，表示“尽管”。
2. no matter wh- 与wh-ever 的联系及区别：no matter wh- 只引导让步状语从句，此时与wh-ever通用。wh-ever又可引导名词性从句，No matter wh-不能。
No matter when / Whenever he comes back, he should be invited to the party.
3. 在条件，时间和让步从句中，用一般现在时表示一般将来时，用现在完成时表将来完成时，
用一般过去时表过去将来时。在since 引导的时间状语从句中，动词一般都用一般过去时，而主句常用现在完成时。
4. 状语从句的倒装一般有下面几种情况：①否定词开头;②so 加adj. 开头;③as /
though引导的让步状语从句。
5. 连词before小结：
We had sailed four days before we saw land. (……才)
We hadn’t run a mile before he felt tired. (不到……就)
Please write it down before you forget it. (趁……)
Before I could get in a word, he had measured me. (还没来得及)
It will be/was…before…要过多久才……
6. because, since, as 引导原因从句的区别：because表达直接原因，语气最强，回答why;
since通常放句首，译为“既然”;as引导不谈自明的原因，语气最弱;
7. as可以引导多种从句，要注意其中的区别。
8. till, until和not…until的区别;if和unless的区别
非谓语动词部分动词不定式几点注意。
1.下列动词或动词短语后接不定式：agree, seem, appear, offer, happen, wish, hope, pay,
expect, long, plan, intend, promise, pretend, decide, afford, manage, choose, be said to,would like to等。
2. 不定式常用的句型：too…to do (太……而不能), …enough to do…(够……就能……), so as to do/in order to do(为了……)，so…as to do/such…as to do(如此……结果……)。
3. 不定式的三个结构：即否定结构、复合结构和疑问结构。
否定结构为“not (never) to do”;疑问结构是特殊疑问词“how (what, which, who, whether…) to do”;复合结构是“for/ of +名词(或代词宾格)+ to do ”。
4. let/ make/ have/ see/ hear/ notice/ observe/ listen to/ look at/ watch/feel
这些动词带不定式作宾补时，省掉to, 若这些动词以被动形式出现时，应加上to。
5. 当前面是the first, the second, the last, need, plan, time, chance, right,determination,ability, opportunity(机会)，way时，一般用不定式作定语。
6. but/ except + to do/ do 结构，要根据谓语动词来确定其后面的形式。当谓语动词是do,does, did时，but后用动词原形;谓语动词是其他动词时，but后用“to + 动词原形”的形式。
7. 形容词后一般用不定式(除busy, worth 两个外)。
You are sure to succeed. 你一定能成功。
He is busy preparing his lessons at present. 他现在正忙于预习功课。
8. 不定式作定语和表语时，有时需要在后面放上一个适当的介词。
This is a bench to sit on.(这是用来坐的凳子。)
This room is comfortable to live in. (这个房间住起来很舒适。)
9. 在“主语+系动词+adj.+不定式”这个句型中，当主语是不定式的逻辑宾语时，不定式不用被动，不能在动词后再放宾语。
The question is easy to answer. (question是answer的宾语，不能说：The question is easy to be answered. 也不能说：The question is easy to answer it .)
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