Ключевые слова: angle, back, blackboard, board, caucasian, chalk, chalkboard, child, childhood, class, classroom, concentration, concept, education, elementary, girl, grade, green, head, indoor, intelligence, kid, knowledge, learn, lesson, math, mathematics, one person, primary, school, schoolchild, schoolgirl, science, scratching, smart, solution, stand, student, study, test, think, thoughtful, tranquility, view, wisdom, work,