Final answer:
Glad hands are the coupling devices used to connect the service and emergency air lines between a truck or tractor and its trailer, designed for an easy and secure connection to maintain proper brake operation.option c is correct.
Step-by-step explanation:
Coupling devices used to connect the service and emergency air lines from a truck or tractor to the trailer are known as glad hands. These are standardized fittings in the trucking industry, designed to allow for quick and easy connection of air lines.
They have a rubber seal that prevents air from escaping and typically come in pairs—one with a color coding of red for the emergency line and another coded blue for the service line. The hands interlock like shaking hands—hence the name 'glad hands'—which seals the connection to maintain the air pressure that is essential for the proper operation of the trailer’s brakes.Glad hands are the coupling devices used to connect the service and emergency air lines between a truck or tractor and its trailer, designed for an easy and secure connection to maintain proper brake operation.