Answer:
The right answer is:
A.It shifted the purpose of the war from preserving the Union to freeing the slaves.
Step-by-step explanation:
Freeing slaves became a legitimate war objective after the Emancipation Proclamation of January 1, 1863. It was made possible only because of Lincoln´s firm commitment to issuing the document and after the Battle of Antietam that allowed the Union to expel the Confederates from Maryland, an event seen as a "victory."