Virginia Code § 38.2-510 regulates unfair claim settlement practices, enforced by the State Corporation Commission’s Bureau of Insurance—a state insurance department (option D). This includes timely claim processing and fair payment, with penalties for violations. Option A (IRS) oversees tax compliance, not insurance claims. Option B (NAIC) develops model laws and guidelines (e.g., Unfair Claims Settlement Practices Act), but lacks enforcement power; states adopt and regulate these standards. Option C (claims adjusters) are practitioners, not regulators. The study guide likely emphasizes Virginia’s Bureau as the authority, citing examples like investigating delayed claims, aligning with state-level oversight under § 38.2-200 et seq., making D the correct regulator.