What are the two types of air lines in a combination vehicle?

Answer: A — Service line and emergency line

In a combination vehicle, the two types of air lines are the service line and the emergency line. The service line is responsible for supplying air to the trailer's brake system when the driver applies the brakes, initiating normal braking operation. This allows for a coordinated and controlled stop across both the tractor and the trailer. The emergency line, on the other hand, is designed to provide air pressure to the trailer’s emergency brake system. If the connection between the tractor and trailer is interrupted, such as a line failure or disconnection, this line automatically activates the trailer brakes to prevent the trailer from rolling away, ensuring safety. Understanding the functions of these two lines is crucial for safe operation and effective braking in combination vehicles. The other options, while they include terms related to vehicle systems, do not accurately describe the critical components that control braking in combination vehicles.