[单项选择]

In the United States, teaching is very important. If teachers do not teach well, students complain. If many students do not understand, people think that the teacher does not do a good job. The teacher has big responsibility to make sure students understand. In a sense, students are consumers and the teacher is offering services.
Students have the right to evaluate their teachers, and they usually do so at the end of each course. That evaluation includes lots of aspects of teaching, such as explanation, preparation, using good examples, answering questions, and organization of classes.
Students are supposed to read required textbooks and recommended books before class. Without reading them, they will find it very difficult to understand the class. Basic courses on doing research and writing papers are taught at the beginning of the program. They teach things very concretely and clearly. Students are expected to apply what they have learned to their studies.

A. giving a lot of lectures to students
B. involving students in discussions
C. asking students questions in class
D. answering students' questions in class