What must be done before instructing an IFR aircraft to change to advisory frequency at a non-towered airport?

The correct answer focuses on the need to provide the pilot with essential information regarding how to cancel their flight plan after an IFR aircraft is instructed to change to an advisory frequency. This is particularly important at non-towered airports where the pilot may need to manage their own traffic and operational communications without the assistance of air traffic control. Confirming that the pilot understands how to cancel their flight plan ensures that there is no misunderstanding about their status and intentions after transitioning to the advisory frequency. It is crucial for maintaining safety and situational awareness in the shared airspace.

The other options, while potentially relevant in different contexts, do not directly relate to the immediate procedural requirement following the advisory frequency change. For example, notifying about weather conditions is important, but it typically occurs during the flight planning and briefing phases. Similarly, providing an altitude to climb to may be relevant during other phases of flight but is not necessary at the moment when changing frequencies at a non-towered site. Lastly, confirming the pilot's intentions could be useful in certain scenarios, yet it does not specifically address the critical need for understanding how to manage their flight plan cancellation after the transition.