Where and why did the major demographic shift of the 1920s take place?

Where and why did the major demographic shift of the 1920s take place?

a. There was a mass movement of people from the cities to the suburbs due to the advent of the automobile.
b. There was a mass movement of people from the rural countryside to cities because consumer industries were located there.
c. The development of mechanization in agricultural production drew populations from urban to more rural areas.
d. People moved from the cities to rural areas to escape overcrowding and poor air quality.
e. Generally speaking, there was relative demographic stability during this period.

ANSWER
B