Answer:
c. Abolished by Constitutional Amendment.
Step-by-step explanation:
Slavery in the United States was abolished thanks to two documents. The first one was the Emancipation Proclamation issued by Lincoln on January 1, 1863. The president used his presidential war powers to proclaim the liberty of slaves that were in the ten states still in rebellion. However, it did not affect the slaves in border states that were still loyal to the Union. What effectively abolished slavery for all slaves was the Thirteenth Amendment to the Constitution.