Ключевые слова: abrasion, background, blackboard, board, border, business, chalk, chalkboard, class, classroom, clean, clear, communication, crack, desk, drawing, education, empty, eraser, flaw, frame, front, grunge, handwriting, illustration, learn, learner, learning, lesson, note, pupil, school, sign, split, stain, student, study, symbol, teacher, teaching, text, university, used, wall, wipe, wood, wooden, work, write,