VLANs (Virtual Local Area Networks) segment network traffic by department, allowing ACLs (Access Control Lists) to be applied based on VLAN membership, improving security and resource isolation. Breakdown of Options: A). VLAN - Correct answer. VLANs enable logical network segmentation, allowing ACLs per department. B). DHCP - Assigns IP addresses but does not control access. C). VPN - Provides remote access, not segmentation within a network. D). STP - Prevents switching loops, not related to ACL implementation. Reference: CompTIA Network+ (N10-009) Official Study Guide - Domain 1.3: Explain VLANs and network segmentation. IEEE 802.1Q: VLAN tagging standard