To the Union, What Did Their Defeat at the First

To the Union, what did their defeat at the First Battle of Bull Run on July 21, 1861, indicate about the Civil War?

A) It was going to need Britain or France to intervene on its behalf.
B) It required more volunteers to fight against the higher number of Confederate soldiers.
C) It decided to focus its war strategy on controlling the Mississippi River first.
D) It had to reconsider that the war would not be as short and bloodless as everyone had predicted.