What defines controlled airspace?

Controlled airspace is defined as airspace with specific dimensions where Air Traffic Control (ATC) services are provided to manage and separate aircraft. This type of airspace is established to ensure the safe and efficient flow of air traffic, allowing ATC to communicate with pilots, provide instructions, and ensure proper spacing between aircraft. The presence of ATC services indicates that pilots operating within this airspace must comply with certain regulations, such as obtaining clearance before entering and adhering to specific routes or altitudes.

In contrast, airspace with no restrictions would not fall under controlled airspace and would instead be classified as uncontrolled. Options that limit operations to only IFR flights or suggest monitoring by radar alone do not capture the full definition of controlled airspace, as it can also accommodate VFR (Visual Flight Rules) operations under ATC supervision.