Which of the following is a legal requirement for seat belts?

All passengers must be buckled up is the correct answer because most jurisdictions have laws that mandate the use of seat belts for all occupants of a vehicle, not just the driver. This requirement is in place because seat belts significantly reduce the risk of injury and fatalities in the event of an accident. Ensuring that every person in the vehicle is properly secured helps maintain a higher level of safety for everyone.

Other options suggest limited requirements or exemptions that do not align with the regulations designed to protect passengers, such as implying that only drivers are accountable for wearing seat belts or suggesting adults can ride without one. Similarly, claiming that children are exempt from seat belt laws does not reflect the serious child safety regulations that enforce the use of appropriate restraints based on age and size.