Final answer:
Brett, the manager of the accounting department, is the best example of a functional manager, as he oversees a specific department within the company.
Step-by-step explanation:
The best example of a functional manager is Brett, who is the manager of the company's accounting department. A functional manager is someone who has managerial authority over an organizational unit—such as a department—within a business and is responsible for the performance of that unit. Brett, as the manager of the accounting department, is in charge of specific functions related to accounting and thus directly fits the definition of a functional manager. In comparison, Mallory is a CEO with a broader role; Rachel, though a supervisor, seems to have a more limited or team-based role; Miguel oversees multiple functions that are more likely aligned with the responsibilities of a general manager or operations manager.