宾夕法尼亚大学法律系教授艾德恩凯迪博士,教书已教了二十年,每学期在他上第一堂课的时候,他总是先在黑板上写下两个数字:四和二。然后他问学生:“结果是多少?” Dr. Adeed Kaidi, a professor of law at the University of Pennsylvania, has taught for two decades and every semester he always writes two numbers on the blackboard when he comes to his first class: four and two. Then he asked the student: “What is the result?”