A、Traveler and agent. B、Manager and worker. C、Shop assistant and customer. D、Classmates. A由对话可知选B，C，D均不正确。

M: Good morning.
W: Good morning, sir.
M: I’d like to enquire about flights to Paris.
W: Yes, sir.
M: Could you tell me how often they go?
W: Let me see. The first one leaves at seven in the morning, and then there’s one every hour till eight in the evening.
M: Sorry, what time does the last one leave?
W: At eight, sir.
M: Thank you.
W: Pleasure, sir.
Q6. What’s the probable relationship between the two speakers?