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' 。
Officials used to have trouble with the foreign names of people passing through Ellis Island, and because they were so busy, many people's names got changed in the rush.
官员们过去总是搞不清埃利斯岛过境人员的外国姓名,因为他们非常繁忙,所以在过境的人蜂拥而至的时候,许多人的姓名都被更改了。