Question

who 与 whom只能who用作主语，whom用作宾语吗？

Answer 1

who 可以做主语，又可以做宾语
whom 只能做宾语

【例子】：
who are you? 不能是whom are you?
This book belongs to whom/who? 两者都可以

简单点说就是：
Whom 只能出现在从句里面或是介词（如 to, from, at, of..）后面。
1． Whom 出现在从句里面时，所有用whom的地方都可以用who代替。Whom 这个词只出现在很正式的书面语。口语不用。
2． Whom 在介词（如 to, from, at, of..）后面时，不可替换。

具体用法：
1. who指人，在从句中做主语
(1) The boys who are playing football are from Class One.
(2) Yesterday I helped an old man who lost his way.

2. whom指人，在定语从句中充当宾语，常可省略。
(1) Mr. Liu is the person (whom) you talked about on the bus.
(2) Mr. Ling is just the boy whom I want to see.

注意：关系代词whom在口语和非正式语体中常用who代替，可省略

Answer 2

who 与 whom都可以用作宾语，但是要作主语，只能用who.,比如在定语从句中