By 1920, more Americans lived in cities than in rural areas. What was one explanation of this change?

Question

A. The growth of railroads caused towns to spring up along their routes.
B. Industries tended to developed and grow in key cities. Factories needed large numbers of workers. People moved into the cities to work in those factories
C. Most farmers moved from rural areas into cities, where they bought small plots of land. They grew food for their own families there.
D. The government wanted cities to grow, so it pad immigrants from Europe to move into cities.