Use D for this item. A switch builds its MAC address table from ingress traffic. When a frame enters a port, the switch records the source MAC address and the receiving interface in the table. In Cisco CCNA 200-301 v1.1, Network Access questions frequently test the practical boundary between similar features: what the feature does, where it is configured, and what problem it is meant to solve. DTP and VTP serve trunk negotiation and VLAN database functions, and egress traffic is not how the switch learns the source location. A clean way to validate the answer is to map the wording of the scenario to the actual device function. If the feature supplies addressing, forwarding, authentication, trunking, route selection, or controller communication, the answer must match that function exactly rather than a nearby protocol name.