Ключевые слова: abstract, background, billboard, black, blackboard, blank, board, business, chalk, chalkboard, cloud, concentrate, concentration, concept, conceptual, copy, design, empty, find, focus, grunge, handwriting, horizontal, information, learning, lesson, magnifier, magnifying, nobody, notice, old, pattern, rays, reminder, search, service, sharp, sign, space, success, target, teach, teaching, texture, used, vision, white, wood, wooden, word,