If you don't know a person's last name, use 'ma'am' or 'sir'.
如果你不知道一人的姓, 你应称呼他为 'ma'am' 或 'sir' 。
John Dewey has said in all seriousness that the part played by custom in shaping the behaviour of the individual,as against any way in which he can affect traditional custom,
风俗在形成个人行为方面所起的作用和一个对风俗的任何影响相比,