Ключевые слова: ad, ads, advert, advertisement, advertising, background, backgrounds, billboard, black, blackboard, blackboards, board, business, chalk, chalkboard, chalkboards, class, classroom, communication, concept, drawing, education, isolated, learning, lesson, marker, message, nobody, note, old, plan, presentation, primary, remember, school, scratch, scratches, sign, space, symbol, teaching, text, texture, textured, textures, white, write, writing,