Why is it important to set your parking brake before leaving your vehicle?

Setting your parking brake before leaving your vehicle is crucial for securing the vehicle and preventing it from rolling. When a vehicle is parked on an incline or uneven surface, relying solely on the transmission to hold the car in place can be insufficient, especially if the vehicle is jostled or if the ground is slippery. Engaging the parking brake helps to stabilize the vehicle, ensuring that it remains stationary even when parked on a slope. This action significantly reduces the risk of accidents caused by rolling vehicles, making it a fundamental safety practice for drivers.

Other options like preventing fuel leakage or ensuring the doors lock properly do not directly relate to the primary function of the parking brake. Keeping the engine cool is also unrelated, as the parking brake does not affect engine temperature. Therefore, selecting the correct answer highlights the importance of safety measures essential for responsible driving.