主語從句三要素：

　　1、關聯詞不能省略

　　2、謂語動詞用單數

　　3、從句用陳述語序

　　常見引導詞

　　what, when, where，which, who, that，whether, how ，whatever, whoever

　　Whether it will do us harm or good remains to be seen.

　　I dont think that whatever happens is right.

　　Is what you told me really true?

　　NOTICE: What we need most are books.