主语从句
主语从句主要有三类：what等代词引导的主语从句；由连词that引导的主语从句；由连接代词或连接副词引导的主语从句。
1．第一类主语从句的关联词what，实际上已成为关系代词(= the thing that)，它所引导的主语从句在结构上相当于名词加定语从句。除what外，whatever也可引出主语从句，含有强调语气，可作主语从句的主语或宾语。
【例句】
They lost their way in the forest, and what made matters worse was that night began to fall.
他们在森林里迷了路，更糟糕的是，夜幕开始降临。(what在从句中作主语)
Whatever we have achieved is attributed to the guidance of our teachers.
无论我们取得什么成绩都归功于老师的教导。(whatever在主语从句中作宾语=Anything that)

【例题】
Although ______ happened in that developed country sounds like science fiction, it could occur else where in the world.
A. which B. what C. How D. it
尽管那个发达国家发生的情况听起来像科学幻想似的，但在世界其他地区也有可能发生。答案B，what引导的从句作主语，表示所……的东西(的情况)。必须注意：what引导的从句是各类的重点，由于what引导的从句本身相当于个名词后加上一个定语从句，所以，在what引导的从句前，一般不可再加上名词或代词。
【实例】
In some countries, ______ is called equality does not really mean equal rights for all people.
A.which B.that C.what D.one
所谓平等在有些国家实际上并不意味着全体人民都享有平等的权利。答案C。
2．由that引导的主语从句在多数情况下都放在句子后部，而用it作形式上的主语。口语中that常省略。如果放在句首主要是为了强调或为了使句子前后平衡。注意此时that不能省掉，前面也不能再加what。
【例句】
That he became a doctor may have been due to his father’s influence.
他成为医生可能是由于他父亲的影响。
It is well known that water is indispensable to life.
It’s a pity that you missed such a fine speech.
这样好的演讲你没听到真是可惜。
【例题】
How did it come about ______ you made a lot of mistakes in your homework?
A.which B.what C.that D. it
你的作业里出现了这么多错误，到底是怎么回事？本句中it是形式主语，that引导的从句是真正的主语，所以答案为C。
【实例】
______ men have learned much from the behavior of animals is hardly new.
A.What B.Those C.That D.Whether
人类从动物的行为中学到了很多东西，这并不是什么新论。答案为C。
3．由连接代词(疑问代词who，whom，whose，which都可用作连接代词)和连接副词(如when，where，whether，how，why等)引出的主语从句放在句子后部时，前面用it作形式上的主语。从句放前或放后，意思基本上没有多大差别。不过whether(or not)引导的从句放在句首或句子后部都可以，而if仅可引出宾语从句，不能放在句首，也不能加or not。
【例句】
Whether (or not) he will go won’t make too much difference.
It won’t make too much difference whether (or not) he will go.
他去不去都一样。
Who will preside at the meeting remains unknown.
谁主持会议还不知道。
How she got wounded at work should be investigated.
她怎样在工作时受伤有待调查。
Why he did such a stupid thing is not known.
为什么他做出如此蠢事还不知道。
Where we should stay is a problem.
我们应该呆在哪里是一个问题。
It is still a question when we shall have our sports meet.
我们什么时候举行运动会仍是个问题。
Whether he will attend the meeting is uncertain.=It is uncertain whether/if he will attend the meeting.
他是否参加会议还不确定。
4．whoever也可引出主语从句，含有强调语气，可作主语从句的主语或宾语。
【例句】
Whoever told you that was lying. 这件事不管是谁告诉你的都是骗人的。