Which of the following is a safety precaution when parking a trailer?

Always using chocks is an essential safety precaution when parking a trailer. Chocks are wedge-shaped blocks placed against the trailer's tires to prevent it from rolling or moving unexpectedly. This is particularly important on inclines or uneven surfaces where gravity could cause the trailer to shift if not properly secured. Using chocks enhances stability and safety, reducing the risk of accidents during the loading and unloading processes or while the trailer is parked.

Other options may contribute to safety in different contexts, but they do not directly address the immediate stability concerns that chocks provide. For example, while ensuring that the trailer is level can help with stability and load distribution, it does not prevent movement. Similarly, turning off the engine before securing the trailer is a good practice to minimize the risk of accidental movement due to unintended ignition or acceleration; however, it doesn't specifically address the trailer's position once parked. Disconnecting the trailer lights is relevant for preventing electrical issues or short circuits, but it does not provide physical support to keep the trailer in place. Overall, chocks are the most direct and effective way to ensure a trailer remains stationary and secure when parked.