Why was slave labor so important to the economy of the Southern colonies?

Slaves provided much of the labor on plantations that grew cash crops.
Slaves provided much of the labor for Southern industries such as ironworking.
Subsistence farmers struggled to grow enough food without the help of slaves.
The slave trade was the most profitable industry in the region.

Question

Why was slave labor so important to the economy of the Southern colonies?

 Slaves provided much of the labor on plantations that grew cash crops.
 Slaves provided much of the labor for Southern industries such as ironworking.
 Subsistence farmers struggled to grow enough food without the help of slaves.
 The slave trade was the most profitable industry in the region.

mathmale · Answer

First of all, what were the primary industries of the Southern states?  Hint:  No ironworking.  Thus, cross out the 2nd answer choice as incorrect.  And so on.