What is the function of the retarder in a vehicle?

1. ATo balance the operation of the engine and regulate the rotation speed of the engine.
2. BTo serve as a substitute for the service brakes (foot brake) in order to stop the vehicle in immediate danger in an emergency.
3. CTo assist the auxiliary brake (parking brake) when parking on a steep descent.
4. DTo slow down the speed of the vehicle while driving not by means of the braking system, for example on a long descent.

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