At what point should an operator lower the trailer's landing gear during uncoupling procedures?

Answer: C — After chock blocks are placed

Lowering the trailer's landing gear after chock blocks are placed is crucial for safety and stability during uncoupling procedures. Placing chock blocks before lowering the landing gear helps prevent any unintentional movement of the trailer. When the trailer is secured with chock blocks, it effectively prevents it from rolling away or shifting, thus creating a stable base for the landing gear to lower onto. This ensures that the trailer will remain in a secure position as the tractor unit is disconnected and eliminates the risk of accidents related to movement. Additionally, executing this step in the described order follows best practices in vehicle safety procedures, reinforcing the structured approach to handling heavy equipment like tractor-trailers. It is essential to ensure that the trailer is fully immobilized before making any adjustments to the landing gear, as doing it in the wrong order could lead to further complications.