What must be verified about the vehicle's emissions system during an inspection?

The correct answer emphasizes that the emissions system must be fully functional and meet the state standards. During an inspection, the emissions system is crucial for controlling pollutants and ensuring that the vehicle complies with environmental regulations. This includes checking components like the catalytic converter, oxygen sensors, and any other parts that play a role in reducing harmful emissions from the vehicle.

Verifying that the system meets state standards ensures that the vehicle not only operates properly but also adheres to legal requirements aimed at protecting air quality. An emissions system that is fully functional contributes to both a vehicle's performance and its compliance with environmental laws, which is a key goal of state safety inspections. This rigorous checking process helps to identify any issues that could lead to excessive emissions, ensuring that the vehicle operates within acceptable limits for public health.

The other choices do not cover the full scope of what is required during an emissions inspection, leaving out critical aspects such as functionality and adherence to established regulations.