How do you properly perform a visual check to ensure the brake lights are working?

You selected answer 1, which is correct. To properly check if both brake lights work, you need to activate first the footbrake and then the handbrake one after another, not simultaneously or just one of them. This ensures that both braking systems are checked individually, so you can see if each brake light functions as intended when each brake is engaged. In practice, to check the brake lights, you can ask someone to look at the rear lights while you press the pedals one after the other, or use reflections to see for yourself. This way, you confirm that the brake lights react to both braking systems, as required by German traffic regulations.