Answer:
C. when the Fourteenth Amendment was ratified
Step-by-step explanation:
Former slaves were granted US citizenship by the Fourteenth Amendment to the US Constitution, which was ratified on July 9, 1868. The amendment overturned the Supreme Court's decision in Dred Scott v. Sandford (1857), which had denied citizenship to African Americans, including those who had been born free. The Fourteenth Amendment's Citizenship Clause granted citizenship to "all persons born or naturalized in the United States," including former slaves. This was a significant milestone in the struggle for civil rights and equality for African Americans.