What must you check before coupling up a multiple-axle trailer?

The selected combination is correct because both checks are essential for safely coupling a multiple-axle trailer in accordance with German traffic regulations.

Firstly, ensuring that the trailer is secured against rolling away is crucial for preventing accidents. This involves checking that the parking brake is applied and utilizing wheel chocks if necessary.

Secondly, verifying that the towing fork is correctly adjusted ensures that the connection between the vehicle and the trailer is secure and safe for towing.

While the condition of the trailer's air brake tanks is important, in the context of coupling, the first two checks are prioritized for immediate safety and operational effectiveness. This understanding aligns with the broader regulations surrounding safe towing practices in Germany.