a friend of Mary's sister 与 a friend of Mary's sister's 有什么区

a friend of Mary's sister 与 a friend of Mary's sister's 有什么区 That girl is a friend of( ) A.Mary's sister' B.Mary sister's The girl talking to Mary is a friend of (Mary's sister's).括号 The girl talking to Mary is a friend of＿. A.Mary's sister B. mary's sister's sister of mary's 那个对 miss smith is a friend of mary‘s mother’s Miss Green is a friend of（ ） A.mary's mother's B.mary's moth Miss Green is a friend of _______.A.Mary’s mother’s B.Mary’s Mr Black is a friend of ____. A. Mary's mother B.Mary's moth a friend of my sister's是什么意思? Miss Smith is a friend of A．Mary's mother's B．Mary's mother 初三一道英语题Miss Green is a friend of（ ）A.mary's mother's B.mary'