英语语法之从句 求大神指教

Question

1、He is no longer the man
that he was fifteen years
ago.
请问为什么是that 不是whom呢？

2、He's what is known as a
“bellyacher”——he's always
complaining about something

请问为什么是what is known而不是
who is known？？

请指教啊！！！凌乱

Answer 1

1、He is no longer the man that he was fifteen years ago.

〔解析〕that 和 who(m) 都可以指代人。who(m) 指代具体的人，that 指代抽象或物化的人。
2、He's what is known as a “bellyacher”——he's always complaining about something

〔解析〕what is known as a “bellyacher" 是表语从句，what 属于关系代词型连词，相当于 “先行词＋关系代词”，即 He's such a person that/who is known as a “bellyacher" (他是大家都知道的那种大声抱怨的人)