Which piece of evidence BEST explains HOW cotton and tobacco led to the expansion of slavery in the South?

A
While New England's development centered on trade, and the middle colonies fed America, the Southern colonies turned to cash crops.
B
Virginia was the first successful Southern colony. Immediately to its north was Maryland. In both colonies, tobacco became the most important crop.
C
The South's focus on growing cash crops led to the development of a slave labor force that was largely unknown north of Maryland.
D
Slaves were present in the North but were much more important to the South. They were the backbone of the Southern economy.