Why Does Medicare's Structure Contribute to Its Spiraling Costs

Why does Medicare's structure contribute to its spiraling costs?

A) Medicare is a single-payer system, so the government both provides the health care and the payment.
B) Medicare operates as a third-party insurer, so it cannot prevent patients, doctors, or hospitals from incurring costs ahead of time.
C) Medicare provides a health care voucher to every beneficiary, and senior citizens lobby to increase the size of their vouchers.
D) Medicare receives a fixed amount of funds every year, so at the end of the year the program spends all of its remaining money rather than return it to the Treasury Department.