This is my opinion: First, the contradiction between teaching and learning, teachers have teaching tasks, and they should clearly and completely convey knowledge to students within the specified time. However, students may not be able to understand or understand the courses carefully prepared by teachers. This is a pair of contradictions. Second, the contradiction between the depth and breadth of lecture knowledge. As a teacher, if you want to speak thoroughly, you must have a certain breadth and foundation. Time is not allowed, and it is common that students may not understand. Third, the contradiction between students' ability to understand. This is a rumor. Of course, there are other contradictions. Among these contradictions, the first pair is the basic contradiction.