Which of the following items must all vehicles have according to safety regulations?

Answer: B — Muffler

All vehicles are required to have a functional muffler as part of their safety regulations. The muffler is a crucial component of the exhaust system, designed to reduce noise produced by the engine while also contributing to the vehicle’s emissions control. Having a working muffler is essential not only for compliance with environmental standards but also for reducing noise pollution in the community. In contrast, while a spare tire can be considered a useful item for emergency situations, it is not mandated by law for all vehicles to carry one. Similarly, an air conditioning system and a sunroof, although often found in modern vehicles for comfort and convenience, are not legally required features. Thus, the muffler stands out as a necessary component that all vehicles must have to adhere to safety regulations.