It is sad that... that引导的是什么从句?

It is sad that... that引导的是什么从句?
为你解答,这是主语从句,IT 为形式主语,真正主语为THAT 后面的从句
类似这样主语从句还有下面的,请主语查看,如果满意,请立即采纳,谢谢!
高中英语14种复合句精品课程讲解
什么叫名词性从句?在句子中起名词作用的句子叫名词从句 (Noun Clauses）
名词从句的功能相当于名词词组, 它在复合句中能担任主语、宾语、表语、同位语等,因此根据它在句中不同的语法功能,名词从句又可分别称为主语从句、宾语从句、表语从句和同位语从句
【一】主语从句【二】表语从句 【三】宾语从句
【四】定语从句 【五】同位语从句 【六】状语从句
【一】主语从句：在主句种充当主语成分的从句叫主语从句,
引导主语从句的连词有：从属连词；连接代词；连接副词
A 从属连词：that,whether.
从属连词；that,whether引导的主语从句在主语从句中不充当任何成分,只起连接词的作用,通常不可以省略.分句置于句首时,that绝对不可以省略.如果是由It作形式主语,后面that可以省略.
1,有that 引导的主语从句如下：
1. That the driver could not control hiswar was obvious.=It was obvious（that）thedriver could not control his car.
2. Thatshe was chosen made us very happy.=it made us very happy that she was chosen
3. Thathe is still alive is sheer luck.=It is sheer luck that she is still alive他还活着全靠运气.
4. Thatthe whole project is doomed to failure is quite clear
=It isquite clear that the whole project is doomed to failure.　很清楚,整个计划注定要失败.
5. Thatyou should have to leave is a pity =It's a pity that you should have to leave.　你非走不可真是件憾事.
6. That he will refuse this piece of advice isimpossible.=It is impossible that he will refuse this piece of advice
7. That they should like each other is natural=It isnatural that they should like each other
8. Thathe will not come to the meeting this evening is true
=It istrue that he will not come to the meeting this evening
9. Thathe will help others is a fact
10. That theearth turns around the sun is known to all.=It is known to all that the earthturns around the sun.
11. That we can win is certain=It is certain that wecan win.
12. That you have made a mistake is a fact.=Itis a fact that you have made a mistake
13. It is ordered that we should leave at once.=Thatwe should leave at once is ordered
14. That you don’t like him is none of my business. =Itis none of my business that you don’t like him
用it作形式主语的that-从句有以下四种不同的搭配关系：
a. It +be +形容词+ that-从句
It is necessary that…　有必要……
It is important that…　重要的是……
It is obvious that… 很明显……
It’s certainthat… 肯定…
It is possiblethat...很可能……
It is unlikelythat...不可能……
It is necessary\important \natural\... that…
It is possible thatshe will come back tomorrow.
It is obviousthat this measure is effective.
b. It +be +V ed 分词+ that-从句
It is known to allthat…　从所周知……
It has been decided that… 已决定……
It is said that………. 据说……
It is known to allthat...众所周知……
It is reported that... 据报道……
It is believed that...据信……;人们相信……
It is suggested that + (should）do... 建议……
It must be admitted that…必须承认……
It cannot be denied that… 不可否认……
It must be pointed out that…需指出的是……
It was reported that 20 people were killed in theaccident.
It was suggested that we should eat more vegetable and do more exercise
c. It + be +名词+ that-从句
It is a pity/shamethat... 遗憾的是……
It is a surprisethat…令人惊奇的是…
It is commonknowledge that… …是常识
It is common knowledge that…　是常识
It is a fact that…　事实是……
It was a pity thatwe lost the match.
It was a fact thathe cheated in the exam.
d. It +不及物动词+ that-分句
It appears that…似乎……
It happens that…碰巧……
It occurred to me that…我突然想起……
It occurred to methat I forgot to send this letter
It happened that I came into the office at that time.
It is important(necessary / advisable /desirable / imperative / true / strange / possible ...)that ...需要注意的是,这类主语从句中,谓语动词很多为"(should)＋动词原形",即要用虚拟语气.例如:
It isnecessary that several nurses (should) stay. 几个护士留在这儿是很有必要的.
It isimperative that everyone (should) learn from practice. 每个人都应该从实践中学习.
It isreported (well-known / hoped / thought / expected / said / believed / decided /suggested / ordered ...)that ...例如:It is said that many people waskilled in the earthquake. 据说很多人在这次地震中丧生了.
itseems(appears / doesn’t matter / makes no difference / ...)that ...
例如:It makesno difference whether he will attend the meeting or not.他是否会参加会议都无关紧要.
当用it作形式主语,而将主语从句放在句尾时,主语从句中的否定词常要前移至主句中.例如:
Itdoesn’t seem that they are from the same university.It doesn’t appear that we’ll have a sunny daytomorrow.
if 不能用在主语从句中,而是用whether,如果主语从句放在句首,不能用if引导,但是如果用it 做形式主语,而把主语从句放在句末时,也可以用if引导.或把if改为whether
If Mary really heard him is really doubtful.
正：It was doubtful if Maryreally heard him. 正:Whether Mary really heard him is really doubtful.
Whether he left (or not) is unknown Whether hewill come is not clear.
Whether it will rain or not) is not clear Whether he’ll come here isn’tclear.他是否会来这里还不清楚.
Whetherwe will go tomorrow )hasn’t been decided yet
Whether the meeting will be put off has not beendecided yet. Whether the policeman willcome is not certain.
Whether the 2000 Olympic Games will be held in Beijing is not known yet.
Whether we’ll go camping tomorrow depends on theweather.whether he likes the job is notclear.
.注意区分it 作形式主语的主语从句与强调句
强调句句型It is/was+被强调部分+that, 去掉It is/was, that,句子仍然成立.
It is natural that they should have different views. 主语从句
It is only lately that he had had a family himself. 强调句
What was it that he wanted?I don’t knowwhat it was that he wanted.
It was in the hotel where he stayed that we discussed the serious problem
8.注意it 作形式主语的主语从句和as引导非限制性定语从句引导的不同
It is known to all that the earth is round. As is known to all. the earth is round.
B连接代词who ,what ,which,whatever,whichever,whoever (Who, whom, which, what可以和ever构成合成词,和what一样引导从句,ever起到强调作用.此类主语从句不能用形式主语it引导,它们在句子中担任成分,不能省略,语序为陈述语序)
What many scientists believe is thatthe earth is round …Who will take part in the meeting has not been decided.
Whoever breaks the law will be punished. Whichstudent will winis uncertain.
Whatever was said here must be kept secret. 这里说的话都应当保密.
Whoever makes mistakes must correct them. 凡犯了错误的人都必须改正.
What is needed for success) is your hard work.Whocan join in the sport meet) is decided by the teacher
What he needs is that book.What he needs are some books.
What he needs are some books.Who he is and where he is from are important.
What he saw are the stars in the sky What he said at the meeting astonishedeverybody present
Whoever leaves the room last ought to turn off thelights.
C连接副词when,where, how, why等.
Why they suddenly disappeared still remains amystery.When they will leave is notdecided.
Where she is from is unknown. How we will paint thehouse has not been decided.
When they will arrive has been told to the teacherWhere we will go tomorrow hasn’t been decidedyet
When he will come is not knownWhen he will come is a puzzle
Where we shall spend the holiday isn’t decided.Where he comes from is a mystery.
Conclusion:主语从句作主语时,谓语动词一般用单数形式
主语从句的规律
规律一、主语从句一律用陈述语序,即主语在前,谓语在后.
规律二、连词that 在从句中无实际意义,但不能省略.
规律三、whether 可以引导主语从句,放在句首,但if不能
规律四、主语从句中的连词不能重叠使用
规律五、含主语从句的主句谓语动词多用单数第三人称形式.
规律六、what 引导的主语从句,可根据表语决定主句动词的单复数形式
规律七、主语从句为了避免头重脚轻现象,用 it 做形式主语,把从句放在后面.