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' 。
When the plane arrived, some of the detectives were waiting inside the main building while others were waiting on the airfield.
当飞机到达时,一些侦探等候在主楼内,另一些侦探则守候在停机坪上。