What role do brakes play on a long steep downgrade?

Answer: B — They are only a supplement to the engine braking effect

Brakes on a long steep downgrade primarily serve as a supplement to the engine braking effect. When descending a steep hill, relying solely on the brakes can lead to overheating and potential brake failure. Therefore, the engine braking effect, which utilizes the engine’s compression to help slow the vehicle, plays a crucial role in controlling speed. By using engine braking first, the driver can maintain a safer speed without overexerting the brakes. This method is vital for preventing brake wear and ensuring the vehicle stays under control on a decline. While brakes are still necessary to adjust speed and ensure safe stopping, they work best in conjunction with engine braking during such circumstances.