Final answer:
The C-300/C-301 Ground-Servicing Unit likely uses a parking brake or wheel chocks to prevent movement during filling operations, ensuring safety during servicing.
Step-by-step explanation:
The component on the C-300/C-301 Ground-Servicing Unit that prevents the vehicle from moving during filling operations is typically the parking brake or a wheel chock system. In ground-servicing units, such safety measures are essential to ensure that the vehicle remains stationary while servicing, which may include refueling, recharging, or maintenance tasks. The parking brake is often integrated into the vehicle's own systems, while wheel chocks are external devices placed against the wheels to physically hinder any movement.