What is the main characteristic of Prohibited Areas in airspace?

The main characteristic of Prohibited Areas in airspace is that aircraft are not permitted under any circumstances. Prohibited Areas are designated by the relevant aviation authorities to ensure the safety and security of sensitive locations, such as military installations or sites of national interest. These areas are strictly off-limits to all aircraft without exception, and any violation can result in significant consequences.

While some airspace classifications may allow aviation activities with special permission, or be associated with military use, what distinctly defines Prohibited Areas is the absolute restriction on flight. Similarly, other options reference concepts related to operational conditions or restrictions, but none convey the unequivocal barring of all aircraft from entering Prohibited Areas. This strict limitation is why option B accurately captures the essential nature of these airspace zones.