Final answer:
Seat belts provide the most protection from being thrown out of the vehicle in a roll-over. They hold passengers securely, preventing ejection, which is their main safety function compared to airbags, crumple zones, and roll bars.
Step-by-step explanation:
The device that provides the most protection from being thrown from the vehicle in a roll-over accident is seat belts. Seat belts are designed specifically to hold passengers in place, preventing them from being ejected from a vehicle during a collision. Airbags, although they deploy upon impact to minimize serious injuries, work in conjunction with seat belts but are not the primary restraining device. Crumple zones are designed to absorb the energy of a collision and thus reduce the force on occupants, but again, they do not prevent ejection. Roll bars help maintain the structure of a vehicle during a roll-over but do not necessarily prevent occupants from being ejected if they are not wearing a seat belt.