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' 。
Against your enquiry, we are pleased to make you a special offer as follows and hope to receive your trial order in the near future.
根据你方要求,我方很高兴就如下商品向你方特殊报价,希望不久能收到你方的试订单。
Doctor, I'm not feeling well, she said. I often feel tired.
“医生,我感到不舒服,”她说,“我经常感到疲倦”。