When driving in a manual truck, how does engine braking work on downhill grades?

Answer: B — It guards against overheating brakes

Engine braking works by using the engine's compression and the vehicle's transmission to slow the truck down. This method is particularly useful when descending downhill grades because it helps reduce the need to rely solely on the brake system, which can overheat and lead to brake failure if used excessively. By downshifting to a lower gear while descending, the driver harnesses the engine's resistance to slow the vehicle effectively, creating a safer driving experience. Using engine braking instead of relying entirely on brake pedals minimizes the chance of brake fade due to overheating and ensures that the brakes remain functional throughout the descent. This is especially critical in large vehicles like trucks, which can carry significant weight and generate a lot of heat when braking.