听力原文： The subjects studied in an American university generally cover a very wide field

. In his first year (when he is called a "freshman") and his second year (as a "sophomore") a student must usually follow courses in a very wide range of subjects in the arts and sciences, including some courses which are compulsory for all students. In his third ("junior" ) year and his fourth year (as a "senior" ) a student may specialize in his main subjects, and he may follow courses of vocational interest. There may, for example, be a Course in poultry marketing and even another in advanced poultry marketing.

In a big university there may be several thousand students taking a compulsory course at the same time. There are various ways of dealing with such a course: we may take as an illustration a sociology course, with say 3,000 students. The students would be divided into about eighty separate classes, each meeting three times a week. There might be a single textbook provided for all the students following the course; or, instead of an ordinary textbook, a specially printed course-book prepared by a committee of the teachers. In preparation for each meeting of the class the teacher might ask the students to read five or ten pages, in order to discuss them and thus find out how well the students had done their work. This is only an example of one method followed: some universities make use of closed-circuit television techniques, including two-way devices, which enable students to put questions to a lecturer in another room. A Maximum of discussion, rather than formal teaching, is widely accepted as an ideal to be aimed at, even amid the difficulties imposed by the great numbers of students involved.

What's a student in his second year called.？

A．Senior.

B．Sophomore.

C．Freshman.

D．Junior.