What action is recommended if a vehicle encounters a steep downhill grade?

When a vehicle encounters a steep downhill grade, shifting to a lower gear is the recommended action because it helps to control the speed of the vehicle without solely relying on the brakes. By using a lower gear, the engine's resistance, or "engine braking," assists in slowing the vehicle down, which can be particularly useful in preventing brake overheating. This action allows for better control and stability, especially on steep descents where brakes can easily become less effective if used continuously.

Other choices, such as turning off the engine or applying brakes continuously, could lead to dangerous scenarios. Turning off the engine would eliminate power steering and brake assist, making the vehicle harder to control. Continuously applying brakes can lead to overheating and eventual brake failure, while maintaining a constant speed may be unsafe depending on the steepness of the grade. Therefore, shifting to a lower gear is a proactive measure that enhances safety while navigating downhill.