The correct answer is A.
OBJ-2.5: A VLAN is useful to segment out network traffic to various parts of the network and stop someone from the open wireless network from logging to the HVAC controls. By utilizing NAC, each machine connected to the open wireless network could be checked for compliance and determine if it is a ‘known’ machine, but they would still be given access to the entire network. Also, since this is a publicly usable network, using NAC could prevent users from accessing all the network features. An IDS would be a good solution to detect the attempted logins, but it won’t prevent them. Instead, an IPS would be required to prevent logins.