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' 。
Some years ago an American psychiatrist named William Dement published experiments dealing with the recording of eye-movements during sleep.
前些年,美国一位精神病学者发表了一篇报告,报告中记录了眼球在睡眠时的活动情况。