Which department has the MOST students for their summer courses in 2017?

The departments are shown on the right of the chart. The history classes are marked in pink, and so you can add up the three classes marked with pink (European History, Civics, American History): 8% + 6% + 9% = 23%
After adding up all departments you will see that history has the highest percentage. The next highest is science, at 22%.