a friend of sb's

a friend of sb's Here's a friend of a friend of Here's a friend of a friend o a friend of Jack还是 a friend of Jack's 介词后面名词的用法a friend of sb's为什么of后面接名词性物主代词,介词后面不要接宾格吗?而且of是.的, a picture of sb; one's picture Is the girl's a friend of? a friend of sb是不是 对sb有好感的人?求问 miss smith is a friend of mary‘s mother’s he is a good friend of of my father's a photo of sb 与 a photo of sb's 有什么区别? a friend of Tom表达对,还是a friend of Tom's对 a friend of Tom,还是 a friend of Tom's 或者两个都对?