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' 。
It suddenly dawned on me that this express was not roaring down the line at ninety miles an hour, but barely chugging along at thirty.
我突然感到这趟快车并没以时速90英里的速度呼啸前进,而是卟哧卟哧地向前爬行,时速仅30英里。