Usually no action is required when a route flaps so it generates the notification syslog level message (level 5).

Add either the ip nat {inside|outside} command under both interfaces.. IP services must be selected by their exact operational role: addressing, translation, time, monitoring, logging, redundancy, or traffic treatment.
Cisco CCNA 200-301 v1.1 includes this under IP Services, where the expected skill is identifying the mechanism that actually satisfies the scenario. The wording usually gives the decisive clue: a protocol number, a route prefix, a control-plane role, a wireless security method, or a management command. The wrong options name real services or commands, but they solve a different infrastructure problem. In a real network, selecting the wrong option would usually produce a failed adjacency, broken client connectivity, insecure management access, or an incorrect forwarding path. The selected answer matches the Cisco behavior and configuration model required by the question, so it is retained as the verified answer for this item.

Explanation: