WHO 可以做主语,又可以做宾语
WHOM只能做宾语
你这道题里,student是was your brother的主语,应该从这方面想
而不是从I though 的宾语这方面想
[解题过程]
who和whom在定语从句中作关系代词时：
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.