Which of the following is a requirement for all vehicles operating on an active airfield?

Answer: C — Must have a ground crewman present

The requirement for all vehicles operating on an active airfield is that they must have a ground crewman present. This is crucial for safety and effective communication on the airfield. The ground crewman acts as a point of contact between the vehicle and air traffic control, helping ensure that there is a clear understanding of the vehicle's movements and intentions. This presence is vital in preventing accidents and ensuring that the driver is aware of airfield operations, such as aircraft movements and active runways, thereby enhancing overall safety on the airfield. While having a certified pilot onboard, being equipped with a radio, or wearing reflective vests can be beneficial and may be required under certain circumstances, the presence of a ground crewman is a fundamental requirement to facilitate the safe operation of vehicles on an active airfield.