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Associated Press
In this Aug. 27, 2012 photo,12 year-old Mark Gregoricka backs up his family's tractor in Springville, Iowa. Scientists at the National Advanced Driving Simulator at the University of Iowa in Coralville this month started what they hope will be a pioneering yearslong research project that aims to learn how cognitive development affects youth driving performance in tractors. (AP Photo/Nati Harnik)

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