What must you do before detaching a semitrailer?

Your answer is correct because all three steps are essential for safely detaching a semitrailer in Germany. First, locking the wheels and extending the supporting legs ensures the semitrailer remains stable and does not roll or tip after detachment. Second, disconnecting all hose and cable connectors between the truck and semitrailer is important to prevent damage to the connections and to safely separate pneumatic, electrical, and hydraulic links. Third, releasing the coupling lock and opening the hitching device allows the truck tractor to physically detach from the semitrailer. Omitting any of these steps could cause unsafe situations or equipment damage, so the full sequence is required according to German traffic and safety regulations.