Answer:
"The factories could be converted to making supplies for the army."
Step-by-step explanation:
The North's factories could be considered an advantage during the Civil War for their ability to be converted to making supplies for the army. This allowed the North to have a significant advantage over the South in terms of industrial capacity and the ability to produce weapons, ammunition, and other supplies for the Union Army. The North's factories also had the advantage of being able to quickly adapt to changing needs and production requirements, which was essential during the fast-paced and dynamic nature of the war. The other options listed (selling surplus goods to Europe for money, getting cotton from the West, and using newly freed African Americans as a cheap source of labor) were not necessarily advantages for the North during the Civil War.