主语从句。
定义：在复合句中充当主语成分的句子叫做主语从句。
主语从句主要有三类：
1)由连词that引导的主语从句。
引导词that无含义，在句中不做成分，不可以省。
that you will win the medal seems unlikely. that you are so indifferent bothers me.
that she survived the accident is a miracle.
2)由连词whether引导的主语从句。
whether有含义(是否)，在句中不做成分，不可以省略。
whether she is coming or not doesn’t matter too much.
3)用连接代词引导的主语从句(在由连接代词who, whose, whom, which, what, whoever, whomever, whichever, whatever引导的名词性从句中，其连接代词在句中起名词性作用，担当一定成分)
what we need is time. what i want to know is this.
whatever you did is right. (主语从句大部分情况看成第三人称单数形式)
what we need are good doctors. (主语从句有时可以根据表语来判断单复数问题)
whoever comes is welcome.
翻译：谁将会成为我们的班长仍然还没有确定。
4)用连接副词when, where, why, how, wherever, whenever引导的名词性从句(其连接副词有含义，在句中作状语)
when they will come hasn’t been made public.
翻译：他们在**举办运动会仍然是个问题。
it作形式主语。
1. it做形式主语，而将主语从句放在句末(尤其是当谓语较短时)
that light tr**els in straight lines is known to all.
it is known to all that light tr**els in straight lines.
when the plane is to take off has not been announced.
it has not been announced when the plane is to take off.
当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 he wants is a book. ≠it is a book what he wants.
2. 当that引导的主语从句出现在疑问句中时，要以it做形式主语，而把主语从句后置。
is it true that tom will give us a lecture next week?
翻译：他们明天不来要紧吗？
does it matter that they will not come tomorrow?
3.当主语从句出现在感叹句中时，要以it做形式主语，而把主语从句后置。
how strange it is that the children are so quite!
4.固定用法。
a. it be +名词(a pity, a fact, no wonder, common knowledge, a question...从句。
it is a pity that we can’t go.
b. it be + adj. (obvious, true, necessary, good, clear, strange...从句。
it is certain that she will pass the exam.
c. it be +过去分词(said, reported, thought, expected, decided, announced...从句。
it is said that tom has arrived in beijing.
it is thought that she is the best player.
d. it seems/ happens等不及物动词及短语+that从句。
it seems that tom isn’t coming to the party.
it happened that i was out that day.
注意：(1)常用whether引导主语从句。
whether she will go home or not is unknown.
2) what与that在引导主语从句时的区别。
what引导主语从句时在从句中充当句子成分，如主语，宾语，表语，而that则不然。
what you said yesterday is right.
that they were sisters was clear.
3)在有些that从句中要用虚拟语气(should do/ should h**e done)
it is strange that he should do that.
it is important that we should attend the meeting.
宾语从句。学习宾语从句要抓住三要素：连接词，语序和时态。
一、定义。宾语从句在复合句中起宾语的作用，可以做动词的宾语，也可以做介词的宾语。
he said (that) he would like to see the headmaster.
二、引导宾语从句的词。
1. 连词：that, whether, if
2. 连接代词：what, whatever, who, whoever, which, whichever等。
3. 连接副词：when, where, why, how等。
三、that
1. that在从句中不充当成分，本身没有词义，可以省略。这类句子通常由陈述句变来。
he says ( that ) jim may fail the chinese exam.
2. that只在except, in和but等少数介词后引导从句做介词的宾语。
we know nothing except that joe is from america.
he differed from other people in that he always looked further ahead in his work.他和别人不同的是他在工作中比别人都看得远些。
i could say nothing but that i was sorry.
3. that在下列情况中不能省略。
a.在连接词and或but所连接的两个作宾语的that从句中，第一个宾语从句中的that可以省略，第二个不能省略。
he said (that) he has worked for nearly ten years and that he wanted to go home.
b.当主句的谓语动词与that宾语从句之间有插入语时，that一般不可省。
just then i noticed, for the first time, that our master was wearing his fine green coat and his black silk cap.
c. 当it作形式宾语时
she made it clear that she had nothing to do with him．
许多带复合宾语的句子，that引导的宾语从句经常移到句子后部，而用it作形式宾语。
四、whether/ if
当由一般疑问句充当宾语从句时，用if或whether引导，意为“是否”。
i don't know if／whether he still lives here after so many years．我不知道这么多年后他是否还住在这儿。
但在下列情况下只能用whether：
在具有选择意义，又有or或or not时，尤其是直接与or not连用时，往往用whether。如：
let me know whether he will come or not．（＝let me know whether or not he will come）让我知道他是否能来。
i don't know whether he does any washing or not．（＝i don't know whether or not he does any washing．）我不知道他洗不洗衣服。
i wonder whether we stay or whether we go．我不知道我们是去还是留。
在介词之后用whether。如：
i'm interested in whether he likes english．我关心的是他是否喜欢英语。
we're thinking about whether we can finish the work on time．我们正在考虑是否能按时完成这项工作。
i worry about whether i hurt her feelings．我担心是否伤了她的感情。
在不定式前用whether。如：
he hasn't decided whether to visit the old man．他尚未决定是否拜访那位老人。
i don't know whether to go．我不知去否。
he hasn't decided whether to go by bus or by train．他还未决定是乘公共汽车去还是坐火车去。
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