It exists to "show that the people created the government and that it exists for the people". A and B don't make sense because we wouldn't want to demonstrate an all-mighty government, because America just escaped from Britain's rule, and the last thing Americans wanted was a president that came off as another king. D isn't a poor answer, but C is clearly stronger and D also isn't too relevant.
The south disagreed with helping the former slaves, so the Freedmen's Bureau promised to help poor whites as well as former slaves, so that the african americans wouldn't have a greater education than any white person.
