Answer:
C. halted the last major Confederate invasion of the North
Explanation:
Gettysburg is located on a very strategic location that connected the north and southern states. If the confederates manage to conquered Gettysburg, they will have more mobility to maneuver their soldiers toward various territories in northern states.
This will gave the confederates massive advantages during the war.
By winning the battle at Gettysburg, the Union forces prevented this from happening and forced the civil war to be conducted on southern ground. On every battle, the damage that's caused by the battlefield keep destroying southern states' economy to the point where they had no choice but to surrender.