You've stopped on a firm, level surface. What's the first thing you must do before you uncouple the trailer? You've stopped on a firm, level surface. What's the first thing you must do before you uncouple the trailer?

• Possible answers:

   
• A. Lower the trailer legs to the ground
• B. Apply the parking brake
• C. Release the brake air lines
• D. Uncouple the electrical lines