名词性从句
第一部分：语法讲解
名词从句是指在句子中起名词作用的各种从句。根据它们在句子中所起的作用不同，名词从句可以分为主语从句、表语从句、宾语从句和同位语从句。
如：That the earth is round is a fact.
I don’t know if he needs my help.
I don’t know where he went.
2．主语从句
1）主语从句在句中作主语。
如：Whether he will accept the invitation is not clear.他是否会接受邀请还不清楚。
When he left is unknown.他什么时候离开还不知道。
That he will come to the discussion is certain.他来参加讨论是肯定无疑的。
2）主语从句放在句首，句子常常显得比较笨重，因此常把它移至句子末尾，而用it作形式上的主语。
如：It is strange that she did not come yesterday. 很奇怪，她昨天没有来。
It has not been announced when the plane is to take off.飞机何时起飞还没有宣布。
It is a pity that Mr.Brown can’t attend our English meeting.真可惜，布朗先生不能出席我们的英语晚会。
3）有些用“it”作形式主语的主语从句结构已形成固定的用法。
a)It is +名词+从句
如：It is a fact that…事实是……
It is common knowledge that………是常识
b)It is +形容词+that从句
如：It is necessary that…有必要……
It is likely that…有可能……
It is important that…重要的是……
c)It is +过去分词+从句
如：It is said that…据说……
It is reported that …据报道……
It is well known that…众所周知……
It is estimated that…据估计……
d)It +不及物动词+从句
如：It seems that …好像……
It happened that…碰巧……
如：It is estimated that millions of galaxies exist in the vast space outside the Milk Way.据估计，在银河系之外的辽阔星空中存在着千百万个星系。
3．表语从句
表语从句在句中作表语，它位于主句中的连系动词后面。结构：主语+连系动词+表语从句。常用的这类连系动词be, seem, remain, look等。
如：The question is whether we can finish our work by tomorrow evening.问题在于我们能不能在明天晚上以前完成这项工作。
That is why she had a day-off yesterday.这就是她昨天请假的原因。
Things are not always as they seem to be.事情并不总是如其表象。
It looked as if it is going to snow.看起来要下雪了。
It may be because he is too young.这可能是因为他太年轻了。
4．宾语从句：宾语从句可以作谓语动词的宾语，也可以作介词和非限定动词（动词不定式、动名词、分词）和某些形容词的宾语。
1）作动词的宾语
如：I know that he is friendly and hospitable.我知道他很友好而且好客。
I asked him if he is sure he knows what he is doing? 我问他是否确信知道自己在做什么？
2）作介词宾语
如：He was interested in whatever he saw here.他对在那里看到的无论什么都感兴趣。
I know nothing about the matter except what you told me.除你告诉我的情况以外，对此事我一无所知。
注：“介词+it+that”结构中，it 可以看成是that 从句的先行词。
如：You may depend on it that they will support you.你放心，他们会支持你的。
I’ll see to it that everything is ready in time.我将负责按时做好一切准备。
3）作形容词的宾语
从句可作有些形容词的宾语。如：sure, certain, glad, sorry, happy, afraid, pleased, surprised等。如：I am sure that she will come and join us.我相信她会来参加我们的活动。
I am not certain whether the train will arrive on time.我没有把握火车是否会准点到达。
He is pleased that he has passed a tough test.他很高兴他通过了很难的测试。
注：
a)在口语和非正式文体中，that 在引导宾语从句时，可以省去。
如：They say （that）he is much better.他们说他好多了。
I am afraid (that) he forgot about it.我恐怕他忘得一干二净了。
b)如果宾语从句后面有补语，要用形式宾语it来代替，而将从句放在补语后面去。
如：He has made it clear that the meeting will not be postponed.他说得很清楚这个会议将不推迟。
We think it wrong that he didn’t help her.我们觉得他不帮助她是不对的。
c)如果主句的谓语是过去时，宾语从句的时态要调整成相应的时态。但是如果宾语从句表示
