What were Southern states required to do before applying for readmission to the Union following the Civil War?

A.
pay reparations to all African Americans in their territory
B.
adopt laws banning discrimination against African Americans
C.
ratify the Thirteenth, Fourteenth, and Fifteenth Amendments
D.
arrest and imprison all Confederate officers and politicians

C. ratify the Thirteenth, Fourteenth, and Fifteenth Amendments