Graue Haare Professor hält Buch und zeigt auf etwas an der Tafel - Stockfoto & -bild

Grey hair professor holding book and pointing on something at blackboard

Rear view of senior lecturer writing something on blackboard with piece of chalk

Cropped image of senior professor pointing on something with pencil on blackboard

Cropped image of professor drawing with piece of chalk at blackboard

Schoolboy pointing at copy space next to chalkboard

Cropped view of man with chalk writing numbers on blackboard

Pensive handsome grey hair man thinking and looking at chessboard at home

African american teacher with pointer standing near working table in classroom

Handsome grey hair man sitting at table and looking at photos at home

Senior man in tweed suit reading notes in notebook with magnifying glass