Ключевые слова: blackboard, board, class, classroom, clip, course, demonstrate, demonstration, diagram, educational, green, group, growing, growth, illustration, image, increase, instruction, isolated, learner, learning, lecture, lecturer, lesson, person, pictogram, presentation, profit, progress, pupil, result, school, seminar, shadow, sign, speaker, speech, statistic, students, study, symbol, teacher, trainer, training, white,