many youths like to hold parties on the day or go to bars to enjoy themslves in two and threes.
问题描述：
many youths like to hold parties on the day or go to bars to enjoy themslves in two and threes.
in two and threes.为什么threes有s啊,two没有啊
答
楼主!
two-and-three 表示2人一组或3人一组 加s 表示对组的复数
有结伴而行的意思.