The correct answer is It promised to transport Southern crops to markets in the North.
Henry Clay's American System focused on three different elements:
1) Implementing tariffs (tax on imported goods) in order to protect American businesses against foreign competition.
2) A national bank that would help with interstate commerce and trade.
3) Government funded programs that would allow for the development of more roads and canals.
The third element of the American system is where Southerners would benefit most. If Southern farmers had more access to roads and canals, they could increase the market for their goods. This means they would have the ability to sell goods (like cotton) to more people than ever before. A larger market for their goods would most likely result in increased profit for the farmers.