Choose the correct, most natural-sounding response according to the context of the conversation:
CLERK: Sure. That'll be $100.
CLERK: They are, but only when you book two weeks in advance.
CLERK: $100. You did want one-way tickets, not round-trip, right?
CLERK: No, I'm sorry, we only accept cash.
CLERK: There's one in the bank across the street from here.