Why were the border states important to the north during the civil war?                 a.  they threatened to form their own country.      b.  they were slave states that could have joined the confederacy.      c.  they had no slave population.      d.  they accounted for most of the farm produce of the north,

 B. They were slave states that could have joined the Confederacy.  

If the border states had joined the Confederacy, it would have greatly bolstered the population as well as the army of the South. However, if the US was more lenient on the border states and allowed slavery there to a certain degree, the Border states would provide a 'buffer' zone to help protect the North from most attacks, as well as provide men for the army and factories for producing much needed supplies.

hope this helps

Cuneiform (a type of writing)