What additional equipment is required on cars manufactured in 1968 and after?

The correct answer highlights the importance of environmental regulations established in the late 1960s aimed at reducing air pollution from vehicles. Cars manufactured in 1968 and later are required to have an exhaust emission system to help control and reduce the pollutants released into the atmosphere, promoting cleaner air quality. This regulation was part of a broader effort to address the growing concerns about air quality and the impact of vehicle emissions on health and the environment.

In contrast, a second muffler, rearview cameras, and anti-lock braking systems were either not mandatory at that time or were not universally required on all vehicles in that era. The implementation of exhaust emission systems reflects a significant regulatory milestone in automotive manufacturing, emphasizing the transition towards more environmentally responsible vehicles.