Which of the following best describes controlled airspace?

Controlled airspace refers to designated areas of airspace where air traffic control (ATC) provides services to ensure the safe and orderly flow of air traffic. In these areas, both aircraft and ATC work together to ensure that flights are coordinated, and air traffic is managed. This monitoring and control help maintain safe distances between aircraft and provide necessary instructions to pilots, ensuring compliance with airspace regulations and procedures.

In contrast, the other options do not accurately capture the essence of controlled airspace. For example, uncontrolled airspace does not involve active monitoring by ATC, and military airspace is specifically designated for military operations, which is distinct from the broader concept of controlled airspace. Additionally, the reference to space above 10,000 feet where no communication is required fails to correspond with the characteristics of controlled airspace, as certain controlled airspace can extend above that altitude and still require communication with ATC.