There is almost no concept of "classmate" in American universities. This is because the university curriculum basically implements the flexible credit elective system, and it is impossible for the school to assign everyone to a class group, so the students in the classroom are very mobile. American university dorms are not divided into departments, students live in scattered places, and students with the same major often don't live together; In the classroom, professors rarely follow the book, and professors interact frequently with students in the classroom. Sometimes when talking about happiness, the professor just sits cross-legged on the platform. After a class, students speak more than professors; There are few "student cadres" in our country. There are not only "secretaries", but also squad leaders, class committees and group leaders. Of course, there is no "student union president" in our habit.