All of the options listed can contribute to explaining the Great Atlantic Migration, but typically, a comprehensive theory would incorporate both economic push factors in Europe resulting from crop failures and economic pull factors in Europe due to industrial growth. These factors explain why people left their homelands (push) and why they were attracted to the U.S. (pull). Additionally, political push factors in Europe due to governmental instability also played a significant role in motivating individuals to emigrate.
If you need to select the primary contributing factor, economic push factors in Europe resulting from crop failures is a strong choice as it directly addresses the hardships prompting migration. However, it is important to recognize that multiple factors intertwined to create a comprehensive understanding of the migration phenomenon.