Which part of the vehicle must be secured after parking?

The correct answer is that the doors must be secured after parking. Securing the doors is crucial for ensuring the safety of the vehicle and its contents. Locked doors can help prevent theft or unauthorized access when the vehicle is left unattended. Additionally, having the vehicle properly secured contributes to overall safety for both the vehicle and surrounding pedestrians.

By contrast, while tightly closing windows is a good practice for protecting the interior of the vehicle and maintaining security, it is not as critical as ensuring that the doors are locked. Passenger restraints do not need to be removed after parking; in fact, leaving them in place is advisable for safety reasons when the vehicle is in use. Thus, the main focus should always be on making sure the vehicle is secured with locked doors.