Provisional license holders are prohibited from operating a vehicle when:

Provisional license holders are required to follow stricter regulations compared to fully licensed drivers, particularly when it comes to passenger safety. The correct choice highlights the critical rule that all individuals in the vehicle, including the driver and passengers, must be properly restrained by a seat belt or child safety seat. This requirement is crucial in reducing the risk of injury during a crash and ensuring that all occupants are safe while the vehicle is in motion.

While speeding, having more than one passenger, and traveling over 40 mph can also be dangerous and against regulations, the specific requirement regarding seat belts and child safety seats emphasizes the importance of safety for all occupants in the vehicle. This rule directly addresses the primary concern of ensuring that the driver and passengers are secured, which is especially vital for provisional license holders who may be less experienced on the road.