Between 1950 and 1973 There Was a Reduction in Income

Between 1950 and 1973 there was a reduction in income inequality. This was in part due to the federal government's progressive income tax policy. In practice, how did this policy work?

A) Income tax was paid depending on the age of the person.
B) Voters paid higher taxes than nonvoters.
C) All citizens paid an equal sum.
D) Wealthy Americans paid higher taxes than others.
E) Immigrants paid higher taxes than citizens.