If the IP phone works but the workstation doesn't, it indicates that the Voice VLAN is functioning correctly, but the Data VLAN (C) is either misconfigured or missing. The workstation typically connects through the phone, which tags voice and data traffic separately using VLANs.
A: Voice VLAN is for the IP phone, which is already working.
B: Native VLAN is for untagged traffic on trunk ports, but doesn't control access directly.
D: Trunk port is more relevant to switch interconnections than individual workstation ports.
# Reference:
CompTIA Network+ N10-009 Official Objectives: 2.3 - Given a scenario, configure and verify VLANs.