The biggest advantage that was held by the North during the Civil war was that the North was fighting to defend themselves. The correct option among all the options given in the question is option "B". Since the North would be defending their territories during the Civil War, so they would not need a longer supply line while the Union would be attacking and they would need a bigger supply line. Bigger supply line meant that the time for the supply to reach would take long and the Union also had to keep the supply line safe. On the other hand, since the North would be fighting in friendly territories, so their shorter supply lines would be easier to defend.