Which type of agent is authorized to perform all acts that the principal can lawfully delegate?

The correct choice is the universal agent. A universal agent is one who has broad authority to act on behalf of the principal, essentially empowered to perform any act that the principal could legally delegate. This includes managing the principal's entire set of affairs, which distinguishes the universal agent from other types of agents.

In contrast, a general agent has a more limited scope of authority, typically granted for a particular business or activity, but not for all conceivable tasks the principal might want to delegate. A special agent is even more limited, as their authority is restricted to a specific task or transaction. Transaction brokers, on the other hand, do not represent one party over the other and facilitate transactions without owing fiduciary duties to any particular party, further narrowing their scope of action compared to a universal agent.