1.定义：用作主语的从句叫做主语从句。
2.构成：关联词+简单句
3.引导主语从句的关联词有三类：(1)从属连词that。如：That they were in truth sisters was clear from
the facial resemblance between
them.很明显，她们确是亲姐妹，她们的脸型很相似。(2)从属连词whether。如：Whether he’ll come here isn’t
clear.他是否会来这里还不清楚。(3)连接代词who,whom,whose,what,which,whoever,whatever,whichever
连接副词 where,when,how,why。如：What she did is not yet known.她干了什么尚不清楚。How this
happened is not clear to anyone.这事怎样发生的，谁也不清楚。Whoever comes is
welcome.不论谁来都欢迎。Wherever you are is my home ---- my only
home.你所在的任何地方就是我的家----我唯一的家。
