Why Was the Battle of Gettysburg So Critical

Short Answer

Why was the Battle of Gettysburg so critical?
A)It was the turning point of the Civil War; after it, the Confederates would never have another victory.
B)It marked the successful crossing of the Potomac River by the Confederate Army.
C)Ulysses S. Grant was finally able to take full control of the Mississippi River.
D)General Robert E. Lee was captured by the Union Army.