SAT Question d3b7d7a3: Transitions answer and explanation

English - Transitions - Elaboration Emphasis Or Specification
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Many historical accounts of the 1930s focus on the widespread movement of people from dust bowl–ravaged Great Plains states to faraway California. However, a 2016 study of 1940 census data complicates this popular narrative; ______ researchers determined, migrants in states hardest hit by prolonged droughts and dust storms—Colorado, Kansas, Oklahoma, and Texas—merely relocated within the region.
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Difficulty:Hard
Which choice completes the text with the most logical transition?