What is a requirement for public inspection stations regarding their location?

Answer: C — They must be located on an all-weather road.

Public inspection stations in Missouri must be located on an all-weather road to ensure consistent accessibility regardless of weather conditions. This requirement is essential as it guarantees that vehicles can reach the inspection station safely and reliably at any time, whether it is raining, snowing, or experiencing other adverse weather situations. Having locations on all-weather roads supports the goal of maintaining safety and convenience for vehicle owners as they adhere to required inspections. Accessibility is a key element of the inspection process, and this stipulation helps facilitate that. The other options do not align with the established requirements; for instance, being on a secluded road or requiring security barriers does not enhance accessibility, and while proximity to major highways might seem beneficial, it is not a mandated criterion for inspection locations.