When the runway is NOT visible from the tower, the transferring controller must ________ before releasing an aircraft to the other's frequency.

When the runway is not visible from the control tower, it is vital for the transferring controller to advise the receiving controller of the aircraft's location. This is crucial because the receiving controller needs this information to ensure safe separation and management of the aircraft once it is handed off. Such communication allows for a smooth transition of control and helps prevent any potential conflicts or misunderstandings regarding the aircraft's position and intentions.

In scenarios where visibility of the runway is compromised, making sure that the receiving controller is fully informed enables them to take appropriate actions based on the latest information. This practice enhances overall safety and operational efficiency in air traffic control, as it ensures that all parties are aware of the aircraft's status.

The other options, while they touch on important aspects of airport operations, do not specifically address the need for informed communication between controllers when visibility is an issue. Providing information about the aircraft's location is the most direct and effective action that supports safe and efficient aircraft operations in such circumstances.