表语从句与主语从句表语从句和主语从句以及宾语从句都要用陈述语序。
Ⅰ.表语从句在复合句中，位于系动词之后作表语的从句称为表语从句。
它位于主句的系动词之后，最为重要的是我们应该为牛找到足够的水。
The doubt is who has taken away the valuable vase. （主语，人）疑点是谁拿走了那只贵重的花瓶。
My topic today is what most scientists are researching.（宾语，物，没有选择范围）我今天的话题就是大多数科学家正在研究的课题。
The problem is which school will be chosen.(which在从句中作定语)问题是哪一所学校将被选中。
All this was over twenty years ago，but it’s as if it was only yesterday.这都是20多年前的事了，但宛如昨天一样。
表语从句中应注意的问题(1)because，why引导的表语从句。
because引导表语从句时，表示“因为”，why引导表语从句时，表示“……的原因”，相当于the reason why。
That’s because he didn’t understand me. (That’s because...强调原因)那是因为他不理解我。
That’s why he got angry with me. (That’s why...强调结果)那正是他对我生气的原因。
(2)what引导的主语从句表示结果或名词reason作主语时，后面的表语从句表示原因时要用that引导，不宜用because。
What cost him his life was that he was too careless.使他丧命的原因是他太粗心了。
The reason why I was sad/for my being sad was that he didn’t understand me.我难过的原因是他不理解我。
(3)使用虚拟语气的表语从句在表示建议、劝告、命令含义的名词后的表语从句中，谓语动词需用“should＋动词原形”表示，should可省略。
常见的词有：advice，suggestion，order，proposal，plan，idea，request，requirement等。
My suggestion is that we (should) have a discussion about this matter instead of just laying it aside.我的建议是我们应当讨论一下这个问题，而不应该把它放在一边。
（4）as if/as though引导的表语从句常置于系动词look，seem，sound，be，become等后面，常用虚拟语气，即形式常用过去式的某种时态。
The elephant feels as if/though it were a wall.大象摸起来像一堵墙。
Ⅱ.主语从句在复合句中，作主语的从句叫做主语从句。
Whether she is coming or not doesn’t matter too much.她来不来都无关紧要。
When they will come hasn’t been made public.他们会什么时候来还未公之于众。
What you need is more practice.你所需要的是更多的练习。
What he is going to be makes me happy.2．it作形式主语that引导的主语从句，that不做句子成分。
在大多数情况下，为了保持句子平衡，用it 作形式主语，而把句子从句放到句末去。
It is likely that there will be a snowstorm tomorrow.明天很可能会有一场暴风雪。
It is a pity that you have to leave so soon.你这么快就得离开真是遗憾。
It is said that he has made much money by selling flowers.据说他靠卖花挣了很多钱。
It seems to me that you object to the plan.在我看来，你好像反对这个计划。
注意：当过去分词为suggested, advised, ordered, requested, insisted, required等表“命令，建议，要求”等意义的词时，that从句中应用“should＋动词原形”，should可省略。
1．(2013·重庆，28) ________ struck me most in the movie was the father’s deep lovefor his son.A．That B．It C．What D．Which解析:考查名词性从句连接词。
句意为：电影中给我留下深刻印象的是父亲对儿子深深的爱。
“________ struck me most in the movie”在句中作主语，且该主语从句中谓语动词struck缺少主语，故选择what (＝the thing that)。
that引导主语从句不担任成分；it不是连词；which“(无论)哪一个”，表示在一个限定范围内进行选择，均不符合题意。
2. (2012·新课标全国Ⅰ，24)It is by no means clear________the president can do toend the strike.A．how B．which C．that D．what解析it是形式主语，空格后是一个主语从句，从句中的动词do缺少宾语，此处所填单词既要引导主语从句，又在从句中作宾语，四个选项中有此功能的只有what。
句意为：总统能采取什么措施来结束这场罢工根本不为人所知。
3. (2012·山东，25) It doesn’t matter ________ you pay by cash or credit card in this store.A．how B．whether C．what D．why解析句意为：在这家商店里，无论你用现金支付还是用信用卡支付都无关紧要。
由It doesn’t matter“没关系”可知后面的意思应该是“无论(不管)……还是……”，又根据题干中的关键词or就很容易确定选B项，构成固定搭配whether...or...。
how如何；what什么；why为什么，均不符合题意。
4．(2012·江西，25) It suddenly occurred to him________he had left his keys in the office.A．whether B．where C．which D．that解析此句考查It occurs/occurred to sb. that...(想到；想起)句型。
that这里是作主语从句的连接词。
5．(2011·山东，26) I’m afraid he’s more of a talker than a doer，which is ________ he never finishes anything.A．that B．when C．where D．why解析句意为：我觉得与其说他是个实干家不如说他是个空谈家，这就是为什么他从来不会完成任何事情的原因。
分析句子结构可知，which引导非限制性定语从句，指代前面的整个句子he’s more of a talker than a doer；在定语从句中，is后面为表语从句，由句意可知which 指代的内容是表语从句内容的原因，故用why引导表语从句。
6. (2014·山东烟台一模)What made the archeologist feel excited was________he finally found two ancient vases in ________seemed to him to be a king’s bedroom.A．that；that B．what；whatC．what；that D．that；what解析：句意：让这个考古学家感到兴奋的是他最终在一个在他看来像是国王的卧室的地方发现了两个古代花瓶。
第一空用that引导表语从句，that在从句中不作成分；第二空用what 引导宾语从句，what在宾语从句中作主语。
D项正确。
7. (2013·宁夏银川一中高三第四次考试) Maybe all Americans realize that________they expect to be the next president will face masses of problems.A．who B．whoever C．whomever D．no matter who解析：考查宾语从句。
句意：或许所有的美国人都意识到无论他们期望谁当下一届总统，他都将面临诸多问题。
“ ________they expect to be the next president”是主语从句，从句中缺少宾语，且此处表示“无论谁”，故用whoever。
8. Why not try your luck downtown, Bob? That is _______the best jobs are.A．where B．what C．when D．why解析：考查where引导表语从句。
句意：Bob，为何不去市区试试运气？那儿是最佳工作所在的地方。
9. ________ in the regulations that you should not tell other people the password of your mail account.A．What is required B．What requires C．It is required D．It requires答案：C。