Ключевые слова: background, blackboard, blank, blue, board, brush, business, chalk, chalkboard, class, classroom, clean, cleaner, clear, concept, delete, drawing, duster, education, erasable, erase, eraser, erasing, hand, isolated, learn, lesson, marker, object, office, pen, presentation, room, rubbing, school, school duster, scrub, space, sponge, stationary, stationery, student, study, surface, teacher, tool, white, whiteboard, wipe, write,