You are driving a motor vehicle with a manual gearbox. What is the correct thing to do when you see this traffic sign?

Your answer is correct because this traffic sign warns of a steep downhill gradient (12% slope). According to German traffic rules, when driving a manual vehicle downhill, you should change down to a lower gear if necessary. This uses engine braking to help control your speed and reduce reliance on the brakes, preventing them from overheating. Changing up to a higher gear or just driving carefully without changing gears is not sufficient or safe in this situation. Always use a lower gear on steep descents to maintain control and safety.