HAD ALREADY BEEN SHOWN 39. TO UNDERSTAND

34. - DETHIHSG COM–DAP AN VA DE THI HOC SINH GIOI MON ANH VAN LOP 10 SO GD
DETHIHSG COM–DAP AN VA DE THI HOC SINH GIOI MON ANH VAN LOP 10 SO GD

34. had already been shown 39. to understand