Final answer:
The agent has violated fiduciary duty.
Step-by-step explanation:
The correct answer is A) the agent has violated fiduciary duty.
Fiduciary duty is a legal obligation that requires the agent to act in the best interests of the principal. In this case, the principal explicitly instructed the agent to market the property only to families on the north side of town. By refusing to comply, the agent has violated their fiduciary duty to act in the best interests of the principal.