Final answer:
ATCFs must notify the Aviation Authorities in the event of unauthorized or suspicious aircraft or UAS activities, as they oversee airspace management and safety enforcement.
Step-by-step explanation:
ATCFs (Air Traffic Control Facilities) are responsible for ensuring the safety and regulation of air traffic. When they encounter a situation involving unauthorized or suspicious aircraft/UAS (Unmanned Aircraft Systems) activity, they should promptly notify the c) Aviation Authorities. Aviation authorities are in charge of airspace management and have the necessary resources and protocols to handle such incidents effectively, including investigation, law enforcement cooperation, and the implementation of countermeasures to maintain safety and security.