A、Wife and husband. B、Teacher and student. C、Clerk and guest. D、Employer and employee. C问题问的是对话者的关系是什么。根据对话内容可知,对话双方为客户与机票订票员的关系

M：Good morning.Will you book a plane ticket to London for me?
W：Yes, sir.What time would you like to leave?
M：The 21st of December.
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 am.
M：Fine.I’ll take that flight, then.
Q15：What does the conversation talk about?
Q16：What’s the relationship between the two speakers?