The correct answer is 'Re-image systems with the clean backup and modify default credentials and access controls before reconnection.' In the case of a persistent threat actor, it is essential to assume that simply restoring a clean backup is insufficient if default credentials or predictable access controls remain unchanged, as the actor could potentially regain access using the same methods as before. The response encompasses not just restoration from a clean backup but also emphasizes altering access mechanisms to prevent the recurrence of the breach. 'Perform a bare-metal restore and immediately reconnect systems to the network' fails to consider that unchanged credentials can be reused by the adversary. 'Install the latest patches prior to re-imaging' is important for system security, but it does not directly thwart an actor who may have knowledge of current credentials or backdoors. 'Integrate additional monitoring tools during the re-imaging process' may help with detection of future breaches but does not necessarily impede the threat actor from accessing the systems using the same methods as before.