Ключевые слова: 3d, art, check, checklist, chemical, chemistry, choice, circle, class, computer, concept, contour, document, eraser, exam, form, green, icon, illustration, internet, isolated, isometric, knowledge, learning, line, linear, lineart, list, mark, online, outline, paper, pencil, plus, questionnaire, round, school, set, sign, student, study, symbol, technology, training, web,