Which documents must you carry?

You answered correctly. In Germany, when operating certain vehicles, you must always carry the permit for use (Betriebserlaubnis), the test certificate (Prüfbescheinigung), and proof of insurance. These documents verify that your vehicle is allowed on the road, confirm you are authorized to drive it, and show that the vehicle is insured. Police can ask for these at any time during a check. Having all three is required to comply with German law and to avoid fines or other penalties.