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 hours, credits, semester course information, students can according to the requirements (such as total credit shall not be less than 60) free elective. Try to design an elective course system, which can provide the following functions