Answer: C. Race no longer barred citizens from voting -> African Americans were guaranteed the right to vote.
Explanation:
The 15th Amendment to the American Constitution was ratified in 1870, after the Civil War and the Reconstruction Era. This Amendment secured voting rights for all Americans, irrespective of "race, color or previous condition of servitude".
The American Congress passed this amendment in order to make it clear that freed slaves had the right to vote (a debated issue at the time).
After the Civil War and during the Reconstruction Era, African American citizens were often denied rights and liberties, based on color of their skin and their race. This amendment stated that race, color or previous condition of servitude wasn't acceptable as a reason for an African American citizen not to vote.