sorry ,i don't know he is a friend of ______为什么选your brother's brothers / brother's friend

sorry ,i don't know he is a friend of ______为什么选your brother's brothers / brother's friend
sorry ,i don't know he is a friend of ______
为什么选your brother's
brothers / brother's friend

sorry ,i don't know he is a friend of ______为什么选your brother's brothers / brother's friend
就应该是your brother‘s ,这种用法是双重所有格结构.
brothers不对,your brother’s friend加个s也行,多个朋友中的一个.

答案错了吧,'s本身有of的意思，这样就重复了，brothers是brother的复述形式，是哥哥的意思， brother's friend 是哥哥的朋友的意思

你可以看看 名词性物主代词 的用法 他这里说的是 你哥哥的朋友http://baike.baidu.com/view/414551.htm