Whose glasses are these?A.It's my father's B.They're my father's

Whose glasses are these?
A.It's my father's B.They're my father's
选B.
glasses 眼镜,如果单数那该是放大镜了
trousers 裤子,如果是单数那该是裙子了
scirrors 剪刀,如果市单数那该是小刀了
哈哈,凯歌玩笑!这样好记而已.