Which two missions does ATC support?

The selection of National Security and Homeland Defense as the missions supported by Air Traffic Control (ATC) is correct. ATC plays a crucial role in maintaining the safety and security of airspace, particularly in the context of national defense. This includes monitoring and managing air traffic to prevent unauthorized access to airspace, safeguarding against potential threats, and coordinating with various defense agencies during national security events.

Furthermore, ATC ensures that any military operations, exercises, or responses are facilitated safely and efficiently, reflecting the critical need for a secure and organized air traffic management system in these contexts.

The other options, while they may involve components of air traffic management, do not encapsulate the primary missions of ATC as effectively. For example, commercial air travel and infrastructure development tend to focus more on the aviation industry rather than the broader scope of security. Similarly, passenger safety and crew training, along with emergency management and environmental safety, while important, do not align as closely with the core responsibilities of ATC in relation to national security requirements.