Play previous course file in the Course File List.

Operation Method:

• Click Previous Button on Main Window; Or
  
  
• Press the shortcut key of "CTRL+B"; Or
  
  
• Click "Menu" -> "Control" -> "Previous";

Notice:

• If the Playing Course File is the first file in the Course File List, this button is not available.
  
  
• This button is not available under Self-defined Study Method mode