What Was One of the Reasons Why the First Battle

What was one of the reasons why the First Battle of Bull Run was significant?

A) Although the North ultimately won the battle, it pushed the North to allocate more resources to the war because the Confederate forces were surprisingly organized, fierce, and resilient.
B) As it was a terrible Union loss, it showed that Lincoln's gravest weakness was his proud inability to acknowledge his mistakes and the speed with which he fell into despair in the face of conflict.
C) As one of the later battles of the war, it showed how the Confederacy had failed at its early plan after its initial battles to make the war as short and decisive as possible.
D) It caused both sides to realize that they were not willing to fight a real war, and as a result, the war ceased for nearly a year before Davis and Lincoln finally decided that there was no way around it.
E) It was a sobering experience for both the North and the South because they underestimated one another's strength, and it became clear the war would not be decided right away as many thought.