WHO 可以做主语,又可以做宾语
但是WHOM只能做宾语
EG：1,who are you?不能是whom are you?
2,This book belongs to whom/who?两者都可以
再举个例子吧
who在定语从句中既能作主语又能作宾语
whom在定语从句中只能作宾语
举个例子吧:
He is the man who(m)I talked to yesterday.
这里who(m)在定语从句中是作宾语,所以两个都能用
He is the man who talked to me yesterday.
这里who在定语从句中作主语,所以只能用who,不能用whom