Final answer:
Controlled airspace refers to airspace classifications where air traffic control services are provided to IFR flights, ensuring safe distances between aircraft in the sky.
Step-by-step explanation:
Controlled airspace is a generic term that covers the different classifications of airspace and defined dimensions within which air traffic control services are provided to IFR flights. The correct answer to the student's question is option c) Air traffic control services are provided to IFR flights. This system of regulated spaces ensures that many planes can fly simultaneously without running into each other. Thanks to the regulations set by the Federal Aviation Administration, each commercial airliner must maintain certain distances both horizontally and vertically from other aircraft, creating an invisible grid in the sky where each aircraft can safely operate.
Additionally, the development of civil airline infrastructure, such as airports with efficient terminals for boarding and luggage handling, supports the safe and regulated flow of commercial passenger air traffic.