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 when he received a similar complaint from another foreigner in the same village, he immediately sent one of his layers to investigate the matter.
但是,当他又收到住在同一村庄的另一个外国人写的一封内容类似的投诉信时,他立即派出一位律师前去调查。