課程開始：表示課程已經開始開放課程資源提供同學學習。
Course start：Course resources are available for student to learn.
課程結束：表示課程已經不允許報名學習，在課程結束之前報名的用戶，（大多數課程）可以繼續讓用戶在課程內學習
若用戶在課程結束之前並未報名，則只能等待下一期開課。
Course end：You can't enroll the course anymore.
If you enrolled the course before it closed, you can still use the resources in the course;
if not, please wait for the course opening again.