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 meal, semester, students may request (such as total credits shall not be less 60) free choices