The correct answer is:
B. Union victories at the Battles of Vicksburg and Atlanta allowed the Union to disrupt major river and railroad Confederate supply lines.
Here's the reasoning: The Battle of Vicksburg was critical because it gave the Union control over the Mississippi River, effectively splitting the Confederacy in half and disrupting their supply lines. The Battle of Atlanta was significant as it was a major transportation hub, and its capture by Union forces further hampered the Confederacy's ability to move supplies and troops. Thus, both victories had a profound impact on the war by limiting the Confederacy's strategic capabilities.