The correct answer is A.
OBJ-4.2: Since this question is focused on the ICS/SCADA network, the best solution would be implementing an Intrusion Prevention System. ICS/SCADA machines utilize very specific commands to control the equipment and to prevent malicious activity. You could set up strict IPS rules to prevent unknown types of actions from being allowed to occur. Log consolidation is a good idea, but it won’t prevent an issue and therefore isn’t the most critical thing to add first. Automated patch management should not be conducted, as ICS/SCADA systems must be tested before conducting any patches. Often, patches will break ICS/SCADA functionality. Anti-virus software may or may not be able to run on the equipment, as well, since some ICS/SCADA systems often do not rely on standard operating systems like Windows.