The Social Security retirement system:

a$.$ is a fully funded pension system.

b$.$ is a tax$-$financed system that pays benefits from taxes that are invested to return principal and interest to

workers when they retire.

c$.$ is a tax$-$financed retirement system that finances pensions by taxing workers each year and transferring the

bulk of revenues obtained directly to retirees.

d$.$ does not use taxes on workers to pay pensions to retirees.