How must a load be marked in darkness or bad visibility when it extends laterally more than 40 cm beyond the side lights of the vehicle?

You answered correctly. When a load on your vehicle extends more than 40 cm beyond the side lights in darkness or poor visibility, it must be marked for safety. The law requires you to use a white light at the front and a red light at the back to clearly indicate the outermost points of the load. This helps other drivers see the full width of your vehicle at night or in low visibility. Switching on the hazard warning lights is not a substitute for this specific marking requirement. Always make sure both the white front light and red rear light are present and visible to comply with the rules and keep the road safe.