A two-axle trailer with overrun brakes and fifth-wheel steering is parked on a slope. How must it be secured against rolling?

Great job—your selections are correct. When parking a two-axle trailer with overrun brakes and fifth-wheel steering on a slope, you must use both the parking brake and a wheel chock under a rear wheel. The parking brake helps prevent the trailer from moving, but the chock is an additional safety measure, especially important on slopes, to physically block the wheels in case the brake alone is insufficient. Supporting the forked draw-bar at the height of the coupling does not secure the trailer against rolling. Always remember: on slopes, both the brake and a wheel chock are required to prevent accidents. This rule is about maximizing safety and stability.