The factor contributing to the shift in population shown on the graph is "Better jobs in industry attracted farmers and farm laborers to cities."
This is evident because there was a boom in the rise of industry in the United States around this period.
This period was after the American civil war and industrial factors such as Railroad construction,
increase in different factories, like steel factories, meatpacking factories, clothing factories, automobile factories, and financial industries.
Hence, in this case, the correct answer is option D. "Better jobs in industry attracted farmers and farm laborers to cities."
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