When must ZAE protect holding pattern airspace?

To determine when ZAE must protect holding pattern airspace, it's essential to understand the role and jurisdiction of air traffic control and how it interacts with arriving aircraft. The correct choice indicates that holding pattern airspace should be protected until the approach controller advises that the arrival is under tower jurisdiction. This is crucial because it ensures that the aircraft in the holding pattern can safely transition to the next phase of its approach without conflicts, as control authority transitions from the approach controller to the tower.

During the time an aircraft is in the holding pattern, ZAE is responsible for maintaining safe separation and avoiding potential conflicts with any inbound traffic. Once the approach controller delegates the responsibility to the tower, the need for protecting the holding airspace is diminished because the tower will manage the incoming traffic.

The other options suggest varying points at which protective measures could be lifted, but they do not account for the critical communication and transfer of control that occurs between the approach and tower. Therefore, the preservation of holding pattern airspace until officially advised allows for safe operations and efficient traffic flow during high-density periods.