What is the main purpose of a truck's engine brake?

Answer: B — To provide additional braking power, especially on downhill slopes

The main purpose of a truck's engine brake is to provide additional braking power, especially on downhill slopes. Engine brakes work by utilizing the engine's compression to slow down the vehicle, which is particularly useful when descending steep grades. This method helps maintain control and prevent brake overheating, which can occur from excessive use of conventional brakes under such conditions. Utilizing the engine brake allows drivers to reduce speed without relying solely on the foot brake, thereby enhancing safety and extending the life of the braking system. By engaging the engine brake, the vehicle can decelerate more gradually and efficiently, which is vital when navigating through hilly terrain.