选课系统：有n门课程，每门课程有课程编号、课程名称、课程性质、总学时、授课学时、实验或商机学时、血粉、开课学期等信息，学生可按要求（如总学分不得少于60）自由选课-Elective System: n course, Course ID for each course, course name, the nature of the course, total hours, teaching hours, the experimental or opportunities hours, blood