What is the primary function of NSL?

Answer: B — It provides air navigation services to UK and international airports.

The primary function of NSL (National Air Traffic Services Limited) is to provide air navigation services to UK and international airports. This encompasses a range of critical responsibilities, including the safe and efficient management of air traffic in both controlled airspace and during the approach and departure phases at airports. By ensuring that aircraft are safely guided through busy aviation environments, NSL plays a crucial role in maintaining a high standard of operational safety and efficiency in the air transportation system. While other options mention activities related to air travel and airport operations, they do not capture the comprehensive role of NSL in air navigation service provision. Operating commercial flights pertains more to airlines, managing ground traffic is a specific airport function often handled by ground controllers, and developing airport infrastructure falls under the jurisdiction of airport authorities and private developers rather than air navigation service providers like NSL. Hence, the correct choice highlights the core responsibility of NSL in the broader context of air traffic management and safety.