The correct answer is "B) The South."
The southern states were heavily dependant on the agriculture industry. They greatly benefited from the "Cotton Boom" during the first half of the 19th century, which made the United States one of the leading cotton producers in the world.
The agriculture plantation system used slaves as the primary workforce. They were seen as an exchangeable resource. As a result, a whole economic activity developed based on the slave trade.
The system ultimately declined with the abolition of slavery.