The instance currently uses an ephemeral internal IP address, which is released and could be reused if the instance is deleted. To ensure the IP is not automatically assigned to another instance, it must be reserved as a static internal IP. Changing the existing ephemeral IP to static (Option C) reserves it, preventing automatic reassignment. Options A and D do not affect internal IP reservation. Option B suggests assigning a new reserved IP, which would change the instance's current IP rather than reserving the existing one.