学生选课系统，其中有老师、课程、学生、选课纪录，可以退订，重选-Elective System students, including teachers, curriculum, students, course record, you can unsubscribe, re-election, etc.

选课系统框架，需要用到的朋友，欢迎下载，包括选课、删除课程等-Elective system framework, need to use friends, welcome to download, including course selection, delete programs, etc.