You're driving a tractor unit fitted with two air lines. You want to couple to a trailer that has three air-line couplings. How should the air lines be connected? You're driving a tractor unit fitted with two air lines. You want to couple to a trailer that has three air-line couplings. How should the air lines be connected?

• Possible answers:

   
• A. The trailer auxiliary line should be left unconnected
• B. The trailer service line should be left unconnected
• C. Only the service line should be connected
• D. Only the auxiliary line should be connected