Final answer:
CMS is not a private insurance carrier, while Cigna, Aetna, and United Healthcare are private insurance carriers.
Step-by-step explanation:
The correct answer is CMS. CMS stands for Centers for Medicare and Medicaid Services, which is a governmental agency. It is responsible for administering the Medicare and Medicaid programs in the United States.
On the other hand, Cigna, Aetna, and United Healthcare are all private insurance carriers. These companies provide health insurance coverage to individuals and employer-sponsored plans. They operate in the private sector and are not government-funded.