单项选择题

Conversation 1
[听力原文]6-7
M: Excuse me, I’d like to go to the Post Office, but I don’t know how to use this ticket machine.
W: Well, just press this button. It is 2 dollars.
M: Thanks.
W: The train is coming soon. Please wait a moment,
M: All right. How often do the trains come at this time of the day
W: Usually it comes about every six minutes.
M: OK, and where should I get off
W: Just get off at the Post Office Station. That’s five stops from here.
M: I’ve got it. Thanks for your help.
W: You are welcome.

How often do the trains come at this time of the day（）

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