Ключевые слова: atom, back, blackboard, board, chalkboard, chemical, chemist, chemistry, class, classroom, demonstrating, discussing, education, exam, explaining, giving, happy, learning, lecture, lecturer, lesson, man, mentor, mentoring, model, molecular, molecule, old, physicist, physics, pointing, presenting, school, science, secondary, showing, student, study, studying, teacher, teaching, thumb, thumbs, trainee, training, tutor, tutoring, university, up,