Answer :
Final answer:
In a tractor-trailer vehicle, it is the air suspension system that allows for unlocking of a control valve so as to adjust changes to the total length of the tractor-trailer and changes in axle load distribution.
Explanation:
To unlock a control valve that allows changes to the total length of the tractor-trailer and changes to axle loads, you would use the air suspension. Air suspensions in tractor-trailers have adjustable controls that enable these changes to occur. Specifically, air suspension uses pressurized air in a bellows arrangement to provide adjustable springing and ride height.
On the other hand, the Fifth Wheel allows the tractor and trailer to pivot independently for better maneuverability, the Landing Gear provides support when the trailer is detached from the tractor, and the Pintle Hook is a kind of tow hitch used in heavy-duty applications but none of them controls the length of the tractor-trailer or the axle load distribution.
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