Ключевые слова: blackboard, boy, casual attire, caucasian, chalk, cheerful, class, classmate, classroom, college, diversity, education, educator, explaining, friendly, gray hair, group, happy, high school, learning, lecture, lesson, male, man, mature, midage, middle school, middleaged, modern, photogenic, school, senior, smile, smiling, student, studying, teacher, teaching, teenage, young, young adult, youth,