Ключевые слова: black, blackboard, blank, board, border, chalk, chalkboard, class, classroom, college, communication, copy space, copyspace, education, empty, formula, frame, hand, lesson, lots, mathematics, maths, note, notice, noticeboard, numbers, participate, plain, reminder, school, scribble, several, sign, signboard, space, sticks, teach, teacher, wooden, writing,