What are the speakers concerned about? A. Finding a parking space B. Missing a flight C. Paying an additional charge D. Avoiding heavy traffic

Question 31 - 33 refer to following conversation:

M-Cn: We're getting close to the airport, so we'd better stop to put gas in the car. The rental company will charge us an extra fee for fuel if they have to do it.

W-Br: Good idea. We don't want to pay more than we have to.

M-Cn: OK, should I take this exit then?

W-Br: No, that's a rest area. Keep going, we want the next exit.

M-Cn: Oh good, and I hope they also sell food. Then we can pick up some snacks for the plane while we're there.

31. What are the speakers concerned about?