Final answer:
A broker working as an intermediary is best described as an agent.
Step-by-step explanation:
An intermediary is a person or institution that stands between two other parties. In the context of a broker working as an intermediary, the best description would be B. Agent.
A broker acts on behalf of another party, connecting buyers and sellers in a transaction. They facilitate the process of buying or selling securities or other assets and earn commission or fees for their services. The broker acts as an agent, representing either the buyer or the seller and working to achieve the best outcome for their client.