The correct answer is A.
OBJ-3.3: Network Access Control (NAC) prevents unauthorized users from connecting to a network. Firewalls and intrusion prevention systems (IPS) are meant to restrict access from external sources and block known attacks. They would not keep out an intruder who is already in range of the wireless network. Network segmentation would limit the access that an intruder has to network resources but would not block the connection itself.