If there is a complaint regarding an insurer and the matter can be cleared by looking at a record of a particular transaction, which of the following authorities would most likely conduct the investigation?

In this scenario, the most appropriate authority to conduct an investigation concerning a complaint about an insurer, especially if it can be resolved by examining a record of a specific transaction, is the Director of the insurance department. The Director holds the responsibility for overseeing insurance practices, ensuring compliance with laws, and protecting consumers. They possess the authority to review transactions and records maintained by insurance companies and can ensure that the insurer adheres to regulatory standards.

State insurance boards typically set policies and guidelines but may not be involved in every individual complaint or investigation. The FBI's jurisdiction is more focused on criminal activities rather than specific insurance-related complaints, while the CPA (Certified Public Accountant) generally deals with financial auditing and does not have the authority to regulate or investigate providers of insurance. Thus, the Director is tasked with handling complaints and is best equipped to address the investigation of insurance-related matters.