Final answer:
Georgia was the last colony to adopt slave labor. Maryland was not considered a middle colony, and Tennessee was not a slave state that remained in the Union during the Civil War. Option b. is the correct answer.
Step-by-step explanation:
By the mid-18th century, the last colony to subscribe to slave labor was Georgia. It was the final colony established of the original thirteen and aimed to serve as a buffer zone against Spanish and French imperial rivals. Initially, James Oglethorpe envisioned Georgia as a refuge for the 'worthy poor' and a substitute for debtor's prison, but it eventually succumbed to the economic pressures of slavery which was a significant part of the colonial economy, especially in areas like Virginia and Maryland.
In contrast, when considering the colonies that were not middle colonies, Maryland stands out. The middle colonies typically included New Jersey, New York, Pennsylvania, and Delaware. Finally, among the slave states that remained in the Union during the American Civil War, Tennessee was not one of them, as it had seceded to join the Confederate States.