A.so that B.that C.what D.in which
解析：what做连接词的时候永远等于“the thing(s) that”，it作形式 主语是只能代名词性结构，代不了“名词+定语从句”的结构。
单个的主语从句作主语时，谓语动词用单数形式；如果是两个或两个以 上的主语从句作主语，谓语动词则用复数形式。
The problem is whn we can get a pay rise.
结构：主语 + 连系动词(be,seem,look) + 句子作表语 (1) 从属连词that，whether, as, as if 等；
The trouble is that I have lost his address.
Where and when he was born has not been found.
When the person was murdered and why he was murdered are still unknown.
Predicative Clause(表语从句)
定义：指在复合句中做主句表语的从句。表语从句和主语指同一内容， 它对主语进行解释、说明，使主句的内容具体化。
It follows that … 由此可见……
It has turned out that … 结果是……
类似的不及物动词还有：seem, appear, occur, follow, happen,turn out, etc.
(由it作形式主语和it引导强调句的比较：
it作形式主语的结构It is+名词/形容词/过去分词+主语从句；而强调 句则不同，它的结构是：It+be+被强调部分+that+从句
He had seen the film before. That is why he did not see it last night.（前面原因，后面结果）
2.在一些表示“建议、劝说、命令”的名词后面的表语从句中，谓语 动词用虚拟语气。should+动词原形表示，should可省略;
My suggestion is that we (should) start early tomorrow.
(3) It is +过去分词+从句 It is said that … 据说…… It is reported that … 据报道…… It has been proved that … 已证明…… It must be proved that… 必须指出…… 类似的过去分词还有：known; estimated; expected; believed; thought; hoped; noted; discussed; required; decided; suggested; demanded; made clear; found out,etc. (4) It +不及物动词+从句 It seems that … 好像是…… It happened that… 碰巧……
(2) It is +形容词+从句 It is +形容词+从句 It is necessary that … 有必要…… It is clear that … 很清楚…… It is likely that … 很可能…… It is important that … 重要的是……
注意:在主语从句 中用来表示惊奇、 不相信、惋惜、理 应如此等语气时， 谓语动词要用虚拟 语气 “(should) +do”，如 strange， natural…
(2)连接代词who, whom, whose, what, which, whoever, whatever, whichever 连接副词 where, when, how, why .
The question is how he did it. That was what she did this morning on reaching the attic.
2.由连接代词who,that引导;
What we lack is experience. Who will go to the energy conference is not important.
3.由连接副词when,how,where,why引导;
How he manages to finish the job is of interest to us. Why he failed the english exam wasn't clear.
注意：that在从句中无词义，只起连接作用；连接代词和连接副词在句 中既保留自己的疑问含义、又起连接作用，在从句中充当成分。
4.当主语过长时，为了符合英语语言的习惯和避免出现头重脚轻的现象 常用it 代替主语从句作形式主语放于句首，而把主语从句置于句末；
It is known to all that light travels in straight lines.
Object Clause(宾语从句)
定义：指在复合句中做及物动词的宾语的从句，也可以做介词和某些形 容词的宾语。宾语从句一般用于及物动词之后，或用于介词之后。
1.由连接词that引导的宾语从句；
由连接词that引导宾语从句时，that在句中不担任任何成分，在口语或 非正式的文体中常被省去，但如从句是并列句时,第二个分句前的that 不可省。
A.it B.it's C.this D.that
解析：如果选B 就成了宾语从句 而宾语从句中，如果主句是一般过去 时，从句要用相应的过去的某个时态。这样时态不对，因此不能选B， 只能选A。
▲宾语从句中需要注意的重点：
★当主句是I/ We think (suppose, expect, believe, guess, imagine) 时，其后的宾语从句如果是否定形式，常把否定词not从从句中转移到 主句中成为否定的转移。
it作形式主语和形式宾语的区别：
I find it necessary to take exercise every day.(形式宾语)
I find it is necessary to take exercise every day.(形式主语)
They found A very hard to work out the problem.
类似的形容词还有：strange; natural; obvious; true; good; wonderful; possible; unlikely; quite; unusual; certain; evident; worth-while; surprising; interesting; astonishing, etc.
(3)A is to B what C is to D. 目的在于突出A对于B的重要
Water is to fish what air is to man. What she wants to know is which dress she should buy. (此处which和what的句子成分是一样的)
英语各种从句的用法
2020年6月
主语从句 表语从句
从句
定语从句 同位语从句
宾语从句
状语从句
Subject Clause(主语从句)
定义：在句中作主语的句子叫主语从句 1.由从属连词that，whether，if引导；
That the plates are moving is beyond dispute. Whether he will come or not is still a question.
It was a great achievement to complete a 24-story building in 10 months.
固定用法和译法: (1) It is +名词+从句 It is a fact that… 事实是…… It is good news that … ……是好消息 It is a question that … ……是个问题 It is common knowledge that … ……是常识 类似的名词还有：a pity,a wonder,surprise,no wonder等.
判断是否是强调句有一个方法，就是将that以后的“句子的其余部分” 拿出来单独看，看有没有缺成分，缺的是什么成分，再把谓语动词后 面that前面的那部分，带到你认为缺成分的地方，如果放进去是一句 完整的句子了，那就说明是强调句。）
It was how the young man had learned five foreign languages __B___attracted the audience's interest.
(3)许多带复合宾语的句子，宾语从句经常移到句子后部，而用it做形式 宾语。结构常是：主语+动词+it+形容词/名词等宾语补足语+宾语从 句
Bad: I thought that he could finish this job in just two hours impossible.
Good: I thought it impossible that he could finish this job in just two hours.
I don’t think he will do so.
★宾语从句中的时态呼应
●主句用一般现在时，从句可用任意时态(主现从不限);
●主句用过去时，从句用过去某个时态(主过从句过) ,但是从句是科学 真理、客观常识、名人格言时用一般现在时;
●情态动词could/would用于，“请求”，表示委婉、客气的语气时， 从句不受主句的约束。