Online learning can go back to the original content, learning from the past, which for someone who does not understand the content, you can go back to school again.
Online learning can be traced back to the original content in the past, which is for people who do not understand the content, they can return to school once.
Online learning can go back to the original content, the past and learn which for people who don't understand the content is able to go back to school again.