Use C for this item. Dynamic auto forms a trunk when the neighboring switch is set to trunk or dynamic desirable. It passively waits for DTP negotiation but will become a trunk when the neighbor actively trunks or requests trunking. 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. nonegotiate disables DTP, while the other command forms are either wrong syntax or unnecessarily active for the stated condition. 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.