A、Wife and husband. B、Teacher and student. C、Clerk and guest. D、Employer and employee. C本题的问题关键词是relationship。根据对话内容，可以推断出对话双方是

M: Good morning. Will you book a plane ticket to London for me?
W: Yes, sir. What time would you like to leave?
M: Next Tuesday, if possible.
W: That’ll be the 21st of December?
M: Yes, that’s right.
W: There are several flights available.
M: Morning flights will be perfect.
W: Yes, sir. There is a flight available on that day, at 10: 00 a. m.
M: Fine. I’ll take that flight, then.
W: 10: 00 a. m. I’ll fix your ticket.
M: When do I check in?
W: You must be there by 9: 00 a. m.
M: Thank you!
9. What is the conversation about?
10. What’s the relationship between the two speakers?