Given the structure and level of gross replacement rates and the expected future growth of

labor earnings subject to the payroll tax, the tax rates used to tax payrolls were increased in

the $1980$s because:

a$.$ the number of retirees per worker will increase.

b$.$ the number of retirees per worker will decrease.

c$.$ wages are expected to decline.

d$.$ the size of the workforce is expected to increase.