I saw a student who I thought was your brother
此处I thought 是插入成分,去掉以后就是这样的,
I saw a student who was your brother.
此处who引导的是定语从句,who作主语,所以要用who.
I saw a student who I thought was your brother
此处I thought 是插入成分,去掉以后就是这样的,
I saw a student who was your brother.
此处who引导的是定语从句,who作主语,所以要用who.