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' 。
but I do not turn for protection to dreary cliches about respect of elders -- as if mere age were a reason for respect.
但我不会用应当尊重长者这一套陈词滥调来为我自己辨护,似乎年长就是受人尊敬的理由。