The correct answer is A) He attacked Confederate lines on all fronts.
What Union General George Meade did that enabled his forces to win at Gettysburg on the third day of battle was "He attacked Confederate lines on all fronts."
The third day of the Battle of Gettysburg was fought on July 3, 1863.
George Meade had been appointed to lead the Army of the Potomac, in the Gettysburg battle. He and his troops repelled the combat of the Confederated troops until the third day. This tactic worked out well, and Meade troops defeated the troops of Northern Virginia, led by General Robert E.Lee. Lee had to retreat.
The other options of the question were B) He hit Lee's forces with artillery. C) He guessed what Lee was going to do. D) He brought in unexpected reinforcements