Ключевые слова: background, blackboard, board, chalk, chalkboard, class, classroom, closeup, college, complex, concept, education, english, exam, formula, formulas, german, grammar, green, handwriting, knowledge, language, learn, learning, lecture, lesson, letter, letters, pattern, process, school, schooling, science, sentence, sentences, sign, study, syntactic, syntax, teach, teaching, training, university, wooden, word, words, write, writing, written,