who 作为主语使用: My father is a doctor who works in a big hospital. 从句结构:who(= doctor, 主语) works(谓语) in a big hospital
whom 作为宾语使用: The girl whom you met is my girlfriend. 从句结构:you(主语) met(谓语) whom(=girl,宾语) He is one of the students to whom i have talked. 这里面whom做介词to的宾语。
The children,all of whom have played for the whole day,are worn out.这里的关系词在从句里是介词of的宾语,用宾格whoThe children who have played for the whole day are worn out.这里的关系词是从句的主语,用主格who追答