Final answer:
Medicare Supplement (Medigap) is a type of private insurance that covers the cost-sharing amounts of Medicare.
Step-by-step explanation:
The type of private insurance that covers the cost-sharing amounts of Medicare is Medicare Supplement (Medigap).
Medicare Supplement insurance plans are sold by private companies to help pay for some of the healthcare costs that Original Medicare doesn't cover, such as deductibles, copayments, and coinsurance.
Medicare Advantage, Medicaid, and Medicare Part D are other types of insurance related to Medicare, but they do not specifically cover the cost-sharing amounts.