参考答案：the students (whom they teach)

解析：细节题。根据最后一段第三句话：most important object of study应该指所教授的孩子、年轻人或成年人，总体来说，这些人都是学生。所以答案应该为：the students (whom they teach)；their students； students to whom subjects are to be taught;“the people whom they teach等。