Ключевые слова: academic, aged, balls, blackboard, board, chalkboard, chemical, chemist, chemistry, class, classroom, college, course, demonstrating, discussing, education, explaining, green, holding, learn, learning, lecture, lecturer, lesson, man, mature, meditating, meditation, old, older, physical, physicist, physics, pointing, presenting, school, science, scientific, scientist, showing, student, study, studying, teacher, teaching, training, tutor, tutoring, university,