单选题 Ray: ______. Where was I?
Brenda: You were talking about your trip to South Africa.
  • A. Let's back up.
  • B. What did I hear?
  • C. Let's check in.
  • D. What were you talking about?
【正确答案】 A
【答案解析】[解析] back这里作动词。back up意为“倒退”；这里引申为“回顾一下”；check in登记，报到，很容易排除。这个短语在酒店常用，相反check out就是退房。其他选项都不能在这个语境中使用。故答案为A。