Undergraduate course is difficult, and the difficulty of junior college can't be compared with undergraduate course. What's more, the chapters in university textbooks are completely out of touch with undergraduate textbooks. High number 1 is the most difficult one for non-mathematics majors in science and engineering. High number 2 is not difficult in economics and management mathematics, and the chapters have changed; High number 3 is the simplest, and it is a major in literature and history.