US Income Data Over the Last 75 Years Suggests That

U.S. income data over the last 75 years suggests that the distribution of income

A) has gradually become more equal over the entire time period.
B) has gradually become less equal over the entire time period.
C) gradually became less equal until about 1970, then became more equal from 1970 to 2011.
D) gradually became more equal until about 1970, then became less equal from 1970 to 2011.