In which area are obstructions not permitted according to safety regulations?

Obstructions are not permitted inside the landing circle due to safety concerns associated with aerial operations, particularly in environments involving aircraft. The landing circle is a designated area intended to ensure that an aircraft can land safely without encountering obstacles that might impede its descent or create a hazard upon landing. Keeping this area clear of obstructions helps prevent accidents or incidents that could arise from any interference during critical operations such as takeoff or landing.

In contrast, other areas mentioned in the choices may have their own safety considerations, but they do not have the same level of criticality regarding airborne operations as the landing circle does. Therefore, maintaining a clear and unobstructed landing circle is essential for the safety of both the personnel involved and the operations being conducted.