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

假定有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，实验或上机学时，学分，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。试设计一选修课程系统，使之能提供以下功能-Assuming there are n courses, each course course number, course name, the nature of curriculum, courses, teaching hours, the experiment or machine hou