听力原文：W: Jack, can you say something about the differences many foreign students encounter in American classrooms?M: One of the first things that happen is that teachers tell the students to call them by their first names. The teacher will then ask the students what they want to be called. Most of them will follow the teacher's example and have the teacher call them by their first names, even if this isn't customary in the country where they come from.W: Do they have a problem with that?M: For some students it sticks in their throat to have to call all their teachers by their first names and some never quite get comfortable with that.W: Are teachers very formal in class?M: Teachers are very easy-going, talking about themselves, their children, their pets. It's a wonderful way of motivating students and getting them to feel good in the classroom.W: The classroom must look informal, too?M: Yeah. The chairs are not organized in rows. They might be organized in a circle or in n semi-circle. There might be large tables in a classroom where students sit in groups around the table. It means that learning is a participatory activity, a two-way interaction.W: With this kind of informality, I guess American teachers don't mind students not being punctual for class.M: American teachers are careful about punctuality. If students don't show up on time, it conveys an attitude of disrespect to the professor.Students are called in American classesA．according to the students' willB．based on the American conventionC．according to their own country's practiceD．at the teacher's will