True $/$ False $/$ Uncertain $(6$ points each$)$

Please answer following $6$ question. In the space provided, please indicate whether the statement is true, false, or uncertain. If true, please explain why the statement is true. If false. please correct the statement so that it is true. If uncertain, provide an explanation of why or suggest what more information is needed.

Managed care organizations help reduce the impact of agency problems that arise in the medical care market.

The overwhelming majority of revenue from Medicare parts B and D comes from payroll tax dollars and beneficiary premium charges.

Any American citizen over the age of $65$ and eligible for Medicare must enroll in Medicare Part A$.$

Goods or services associated with a negative externality are overproduced.