What is true regarding downshifting for a long downhill grade?

Answer: C — It allows engine compression and friction to assist in slowing the vehicle

Downshifting for a long downhill grade is an essential technique for maintaining control of the vehicle. When a driver downshifts, the engine speed increases, which allows for better engine braking. This process utilizes engine compression and friction to assist in slowing the vehicle down; as the gears are shifted to a lower ratio, the engine provides resistance against the forward motion. This mechanical assistance is crucial, especially on long descents, as it helps prevent the brakes from overheating and losing effectiveness, thus enhancing safety. In addition, using engine braking through downshifting helps maintain a controlled speed without relying solely on the brake pedals, promoting better vehicle handling and stability during a downhill descent.