A. 英语语法 关于If引导的条件状语从句或虚拟语气
If i were on the spot that day,I would have been able to prevent the disaster from happening,
这句话地意思是：如果那天是我在当班，我就能够阻止灾难的发生了。
这里用的的确是虚拟语气，虚拟的也是过去的时刻发生的事，但是并不是过去的事情都得用过去完成时来表虚拟，这里用were 并没有错
但是 你如果用完成时也是可以的：If i had been on the spot that day,I would be able to prevent the disaster from happening,这个句子也是对的
这两个都是虚拟的过去，但是并非二者选其一，两个都是对的啊
你举得这个例子：If I were not busy, I would have come.也表过去
如果我不忙（过去的某个时间），我就去了
下面这两个句子应该会对你有启发：
If I were you, I would have taken his advice.我要是你，我就采纳了他的建议。（从句指现在，主句指过去）
If the weather had been more favorable, the crop would be growing still better.如果气候更适宜一些，庄稼会长得更好。（从句指过去，主句指现在）
ps：if I were you ，I would take this answer.
希望采纳
B. 条件状语从句、时间状语从句、宾语从句的语法（要全）急急急！！！！
你好,以下是你要的最全面的资料,对你定有帮助.
一. 时间状语从句:
学习状语从句的重点是连接从句的连词的选择，就比如时间状语从句吧。
The new secretary is supposed to report to the manager as soon as she________.
A.will arrive B.arrives C.is going to arrive D.is arriving
在时间状语从句中，当主句是将来时或含有情态动词时，从句通常用一般现在时代替将来时。选（B）每当他们遇到困难时，我们就去帮助他们。
We will go to help them whenever they meet with difficulties
可以引导时间状语从句的词很多，比如when ,wile,as等等。
When ,while,as的区别
I was reading a novel________he watching TV.
A.when B.while C.before D.as 2
While表示一段时间并表示对比，从句中不能用点动词；when还可以表示从句动作发生在主句动作之前或之后；as表示“一边。。。。。一边。。。。。”
While表示对比不只可以用在时间状语从句中。
Some people like coffee,while others like tea.有人喜欢咖啡，而有人则喜欢茶，强调了对比。When you have finished your work,you may have a rest.当你工作做完的时候，你可以休息一会儿。从句的finish发生前，才会有rest(休息)这个动作发生。在这种情况下，就只能用when,而不能用while或as,除此以外，when还有一点比较特殊。
When可以表示“那时突然”的意思，而其他两个词则还可以，比如说，我在看电视的时候，他突然进来了，就可以说：I was watching TV,When he suddenly came in.
As通常表示“一边。。。一边”的意思，比如我边洗碗边唱歌就可以说“As I was washing the dishes,I was singing songs.”另外，它还可以表示”“随时间推移”，这就是它的特殊之处了。
You will grow wiser as you grow older.
引导时间状语的从句还有before,after,once,until等。这个until的用法也需要注意，下面我们就来看看它该怎么用吧。
People don’t know the value of freedom________they have lost it.
A. until B.when C.since D.as
till和until表示“直到。。。。。。才。。。。。。”要和延续性动词连用，not….until是固定搭配。
Not….until……√ not….till,而且until可用于句首，而till通常不用于句首，比如：Until you told me,I had heard nothing of what happened。
直到你告诉我，我才知道出了什么事
还有几个连接时间状语从句的关联词，表示“一…..就。。。。”的结构，他们是：as soon as,the moment,no sooner….than ,hardly/scarcely….when. Tony,这些关联词你用用吗？
值得注意的是这几个关联词的量才而为和语序的不同用法。量才而为上，as soon as和the moment所在的复合句中，主句和从句通常都用过去时，no sooner…..than和hardly/scarcely…when所在的复合句中，主句一般用过去时，而从句用过去完成时。
________had he gone to bed. ________he fell asleep.
A. The moment,/ B.No sooner,than C.When,hardly D.As soon as,/
当no sooner或者hardly在句首时，从句要倒装。
我刚一到家，就开始下雨了。
As soon as I got home,it began to rain.
The moment I got home,it began to rain.
Ihad no sooner got home than it began to rain.
Hardly had I got home when it began to rain.
no sooner….than和hardly….when说一下，至少要一句倒装啊。
二、条件状语从句。
You will be late__________you leave immediately.
A. unless B.until C.if D.or
B.
Unless=if not. If you don’t leave immediately you will be late.
在条件状语从句中，如果主句是将来时或含有情态动词，从句通常用一般现在时代替将来时。这只有在时间和条件状语从句中才有这个用法。
条件状语从句还可以由as long as(只要),in case(以防)，on condition that(条件是)等词来引导。
You may do anything you like as long as it is not against the law.只要不犯法，你可以做任何你喜欢的事。
Take this umbrella with you in case it rains.带上这把十倍雨伞，以防下雨。
三、宾语从句
引导宾语从句时，whether和if一般可以互换。If和whether直接就可以引导宾语从句了，不用that了。
可是并不是在所有的宾语从句中if和whether都可以互换。它们也是有区别的。
如果出现or not则只能用whether。
比如：We don’t know whether he will come or not.我们不知道他是否会来。在这句话里只能用whether.
介词宾语从句只能用whether。
比如：That depends on whether he will come.那取决于他是否会来。
宾语从句还有和主语从句不一样的地方。我们看一看吧。
8.________ I should take part in the sports meet?
A.Do you think why B.Do you think when C.Do you think D.Do you think how
C
引导宾语从句的that在从句中不充当任何成分时，可以省略。
不过不是所有引导宾语从句的that都可以省略。
第一，如果有两个并列的由that引导的宾语从句由and或but连接，那么第一个that可以省略，但第二个that不能省略。
比如：He said(that)he liked to live in China and that he wouldn’ t leave for America.
他说他喜欢住在中国而不会去美国。
第二点是如果that引导的是介词宾语从句，则that不能省略。
例如：你的作文写得不错，只是有几个拼写错误。就应该说
Your composition is quite good except that are some spelling mistakes.
这里的that引导的从句作介词except的宾语，连接词that就不可以省略。
也就是说主语从句的that不可以省略，而宾语从句的that却在大多数情况下可以省略。
主语从句和宾语从句也有相同的地方。
名词性从句之间是有些共性的，下一个秘诀和主语从句的也很相似。
9 We think________important that college students should master at least one foreign language.
A.it B.him C.that D.what
A
主句的宾语是“宾语＋宾补”的复合宾语时，要用形式宾语it替代宾语从句，而将宾语从句置于宾补之后。
再比如：我认为所有的人都应该尊重老人，这是非常正确的。
I think it quite right that all of us should respedt the old.
10.I don’t think you are right,____?
A.aren’t you B.are you C.do I D.do you
B
这是通过反意疑问句来说明宾语从句的否定情况，动词think, believe, suppose, expect等词后面的宾语从句带有否定含义时，通常不否定宾语从句中的谓语，而是否定主句的谓语动词。
这种下的反意问句要根据从句的真正意思来提问。
再来练习一下。
我想他不会来 I don’t think he will come.
11.No one can be sure________in a million years.
A.what man will look like B.what will man look like
C.man will look like that D.what look will man like
A
Sure,afraid,glad,certain等形容词后面可以接宾语从句。
这几个形容词的后面通常都是接介词of的。
比如I’m afraid of being late.如果转换成宾语从句就是I’m afraid that I’ll be late.
再比如I am sure that you will come.我确信你会来。
宾语从句：陈述语序
形式宾语
if和whether的区别
在某些动词和形容词后的用法
C. 英语的条件状语从句咋写
条件状语从句可分为真实性和非真实性（虚拟语气）两种。
真实性条件状语从句：内主句用一般将容来时，条件状语用一般现在时，if
it
rains
tomorrow
we
won't
go
to
the
beach.也不是绝对的，也有一些变形
主句也可以是祈使句，例如please
come
to
my
party
if
you
have
time.
主句也可是情态动词，例如you
can
take
a
nap
if
you
are
tired.
从句也可是现在进行时例如，if
he
is
working
i
won't
disturb
him.
D. 英语中：条件句和条件状语从句区别
没区别的。
条件句就是条件状语从句，条件句不可能当主句。
E. 英语中条件状语从句分几种
状语从句分九种，条件状语从句应该分真实条件和虚拟条件吧
F. 英语中什么是条件状语从句
由连接词if或unless引导的状语从句叫做条件状语从句。
引导条件状语从句最内常用的连词是if，由if引导的容条件状语从句表示在某种条件下某事很可能发生。例句：If
I
want
an
apple,
my
mother
will
give
one
to
me.
除了if之外,还有很多词引导条件状语从句，但是出现的频率较小，就几个例子吧：
unless
除非,若不,除非在……的时候;
on
condition
(that)...
在……条件下,如果;
supposing
如果,假如;
provided
假如,除非,以……为条件.
G. 英语中的条件状语从句
连接词主要有
if,
unless,
as/so
long
as,
on
condition
that
等。.
if
引导的条件句有真实条件句和非真实条件句两种。非真实条件句已在虚回拟语答气中阐述。
unless
=
if
not.
Let's
go
out
for
a
walk
unless
you
are
too
tired.
If
you
are
not
too
tied,
let's
go
out
for
a
walk.
典型例题
You
will
be
late
___
you
leave
immediately.
A.
unless
B.
until
C.
ifD.
or
答案A。
句意：除非你立即走，否则你就回迟到的。可转化为
If
you
dong
leave
immediately,
you
will
be
late.B、D句意不对，or表转折，句子如为
You
leave
immediately
or
you
will
be
late.
H. 英语if引导的条件状语从句重点
学习" if " 引导的条件状语从句的用法,现在总结一下:
if 条件句不一般,几个要点记心间;
条件句,放在前,逗号要放句中间。
条件句表可能，主句多用将来时；
条件句表事实，主句常用现在时。
在 if 引导的条件状语从句中，如果从句谈论的是一个有可能发生的事实及其产生的相关的结果，主句用一般将来时态，从句用一般现在时态。如：
We can walk there if we can't find a bus .
If it rains tomorrow ,we will not go to the zoo.
What will you do if you find a panda in danger.
如果 if 条件句谈论的是重复发生和预示要发生的情景和事件，则主从句大多用一般现在时态。如：
If bears are in danger ,they attack people.
注意 ：
在 if 引导的条件状语从句中，if 和条件句位置灵活，可直接放在主句后面，若 if 条件句放句首，
从句后面要加逗号，和主句隔开。
还要注意前后时态一致原则
I. 英语中从句的语法大全
英语中六大从句用法总结
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...
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。
*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。
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.
5.定语从句
定语从句所修饰的先行词可以是名词或代词，也可以是一个句子。定语从句通常位于先行词之后，由关系代词或关系副词引导。
*限制性定语从句
限制性定语从句修饰先行词，对先行词起修饰作用，紧接先行词之后，无逗号，若省去，原句意思不完整。引导定语从句的关系代词有who,whom,whose,which,that等。who,whom,whose用于指人，whose有时也可指物，相当于of which；which用于指物；that既可指人也可指物，但只用于限制性定语从句中。关系代词除了引导定语从句，替代先行词外，还在从句中担任主语、宾语、定语等。
The computers and cables which make up the Internet are owned by people and organizations.
Those who live alone or who are sick may have trouble in getting close to other people.
The girl whose parents died in an accident is living with her grandmother.
1)当先行词是all,anything,everything,something,nothing等不定代词或先行词前有first,last,any,few,much,some,no,only以及形容词最高级修饰时，只能用关系代词that引导从句。
That is all that I've heard from him.
He's the first person that I'm going to interview this afternoon.
2)关系代词的省略
在从句中作宾语的关系代词常可省略。关系代词紧跟介词，作介词宾语时不可用that，只可用which或whom引导从句，并且不可省略，但当介词位于宾语从句句末时，作为介词宾语的关系代词仍可用that，也可省略。
This is one of those things with which we have to put up.
This is one of those things (which\that) we have to put up with.
3)引导定语从句的关系副词有when,where,why等。关系副词在从句中作状语，意义上相当于一个“介词+which”的结构。
Even in comic books where(=in which) there are no words,the stories are fully expressed through the drawings.
No one knows the reason why(=for which) he was so angry that day.
5.定语从句
*非限制性定语从句
非限制性定语从句既可修饰先行词，也可修饰整个主句，起补充说明作用，与主句之间有逗号隔开，若省去，原句意思不受影响。不可用that引导非限制性定语从句。关系词不可省略。
Every object has a gravitational pull,which is rather like magnetism.
*“介词+which\whom\whose”引导的定语从句
“介词+which\whom\whose”可引导限制性定语从句，也可引导非限制性定语从句，该结构中介词的选择取决于从句谓语动词的固定搭配，或先行词的习惯搭配。
This is the computer on which he spent all his savings
It is written by a person with whom we are all familiar.
*as引导的定语从句
as引导的定语从句主要用于“such...as”及“the same...as”的结构中，代替先行词是人或物的名词。as引导非限制性定语从句时，代替整个主句，从句可位于主句之前、之后或中间。
These are not such problems as can be easily solved.(as代替先行词problems)
As is mentioned above,no single company or group can control what happens on the Internet.(as代替主语)
6.状语从句
*时间状语从句
引导时间状语从句的从属连词和词组有：
1）when,whenever,while,as,after,before,since,till,until,once等。
We have learnt quite a lot about it since we came here.
2)as soon as,hardly(scarcely)...when,no sooner...than,each(every) time,the moment,immediately(that)等。
As soon as I sent an e-mail message,I received positive responses.
The moment he heard the good news,he jumped with joy.
*地点状语从句
引导地点状语从句的连词是where,wherever.
Wherever she went,she took her little daughter with her.
*原因、结果和目的状语从句
1）引导原因状语从句的从属连词有：because,as,since,now(that),seeing that,considering that,in that等。
Considering that he is a freshman,we must say he is doing well.
2)引导结果状语从句的连词有：so...that,such...that
,so that,that,so等。
Mickey Mouse is so attractive that the children are reluctant to leave.
3)引导目的状语从句的连词有：so that,in order that,for fear that,lest等，从句常使用may,might,can,could,would等情态动词。
We got up early this morning so that we could catch the first bus to the railway station.
*条件和让步状语从句
1）引导条件状语从句的连词和词组有if,unless,as(so) long as,on condition that,in case,provided(providing) that,supposing等。
As long as you have the right equipment,you can use a telephone line to transmit computer data.
2)引导让步状语从句的连词和词组有though,although,whether,even though,even if,no matter what(when,how...),whatever(whenever,wherever,however....)等。though,even if等引导状语从句可转换成含有as的部分倒装结构，具有强调意义。其结构为“形容词（副词、动词、名词）+as+主语+谓语”。
No matter what you may say,I would not change my mind.
Young as he is,he is quite experienced in this work.(=though he is young)
Child as he is,he can speak English fluently.(=though he is a child)
*方式状语从句
引导方式状语从句的连词有as,just as,as if,as though等。as if,as though引导的状语从句中，谓语动词常用虚拟语气，表示与事实相反。
The young man made the experiment just as the teacher had taught him.
Everything went on as usual as if nothing had happened.