The correct is A) it controlled Vicksburg and other forts.
During the Civil War, one advantage that the Confederacy had over the Union was that the Confederacy controlled Vicksburg and other forts.
This was so important for General Robert E. Lee and other military men during the Civil War because it represented an advantage over the Union's troops in the south. Fort Donelson and Fort Henry also were under the control of the Confederates. The Union Army had to recapture the forts to change the situation. Mostly the did so when they won the Battle of Vicksburg on July 4, 1863, and could control the ports of the Mississippi River.
The other options of the question were B) It had a fleet of armored gunboats. C) It outnumbered the Union troops. D) It had the support of European nations.