Upward structural mobility happened to masses of workers who came to form the middle classes.
A. After WWII, especially in the north and north-central states
B. Among many of the poor, as a result of President Johnson's "War on Poverty"
C. In the southern U.S. starting in the late 1960s but especially during the 1970s as a result of capitalization by northern and foreign corporations
D. All of the above