Answer :
Final answer:
In a combination vehicle, a major air leak in the supply line will cause the tractor protection valve to close. This valves protects the tractor's air supply. Meanwhile, the drop in pressure also triggers the emergency brakes on the trailer.
Explanation:
In a combination vehicle, the tractor protection valve is designed to prevent air loss from the tractor if the trailer becomes disconnected or a major air leak occurs in the trailer system. When the air pressure drops below a certain level in the supply line, this automatically activates the valve to close, thus protecting the tractor’s air supply. The decrease in pressure simultaneously engages the trailer emergency brakes to stop the vehicle. So, the entity causing the tractor protection valve to close and the trailer emergency brakes to come on during a major air leak is (a) The supply line.
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