add and delete
Revert "add and delete"

This reverts commit 8d8a801b369893211cac1124efbf309e3573a2dc.
Revert "Revert "add and delete""

This reverts commit ad595bf207a4f8d1b5e9c35299e09c427f224da0.
Merge remote-tracking branch 'origin/master'

Conflicts:
	js/back_end.js
Merge branch 'master' of https://github.com/winterJIE/school