What should a driver do before going down a steep grade with a heavy vehicle?

Answer: C — Shift to a lower gear

When preparing to navigate a steep grade with a heavy vehicle, shifting to a lower gear is crucial. This action helps to increase the engine's RPMs and utilize engine braking, which is essential for maintaining control and reducing the reliance on the brakes. Heavy vehicles have significant momentum due to their weight, and relying solely on brakes can lead to overheating and potential brake failure, especially on long downhill stretches. By shifting to a lower gear, the transmission engages a gear ratio that allows the engine to help slow the vehicle down, thereby providing additional resistance against gravity. This practice enhances safety by allowing the driver to manage the vehicle's speed more effectively and reduce wear on braking components. It is a key aspect of driving safety for heavy vehicles, as it helps to prevent accidents and maintain stability while descending steep grades.