translation.en: So if you're smart, you tend to be friends with smart people, and if you're young, you tend to be friends with young people, and this is well established for hundreds of years.
translation.zh: 所以说，如果你很聪明，你倾向于和聪明的人交朋友。 如果你还年轻，你倾向于和年轻人交朋友。 这是数百年来 公认的理论。