名词性从句
在句子中起名词作用句子叫名词性从句.
1宾语从句；2主语从句；3表语从句；4同位语从句
主语从句
在另外一个句子中做主语句子叫主语从句。
How the book will sell depends on its author.
That he is the best student in the class is obvious
主语从句惯用it作形式主语放句首
因而我们常见到这种句式：It+be+n./adj/-ed从句（that, whether,etc.)例：It's a pity that you should have  to leave. = That you should have to leave is a pity.It is great that I have a teacher like you.= That I have a teacher like you is great.