Use B for this item. 802.11a operates in the 5-GHz band and is useful when more nonoverlapping channels are needed than 2.4 GHz can provide. It is not compatible with 802.11b/g clients because those standards use 2.4 GHz. 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. Microwave-style interference is mainly a 2.4-GHz concern, and cost is not the reason to choose 802.11a over b/g. 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.