Why did the cost of slave labor double even after the invention of the cotton gin?

a.
the demand for enslaved workers for the cotton fields was high, but the supply of workers was low due to the ban on the slave trade.
b.
northern enslavers refused to sell their enslaved workers.
c.
enslaved workers were in high demand for tobacco and rice farms.
d.
more enslaved workers were being freed at that point so that they could return to africa.

The cotton gin did reduce the need for slaves for removing slaves, it did not reduce the need for slaves to pick cotton. To be honest, it actually doubled it by mistake.  Cotton had become so profitable that for planters it had increased the demand for cotton.

pleas go answer my queston befor i fial my test

either b) they were often feared and despised by other native cultures. or

c) their obsession allowed them to coexist with many other native cultures because of their peaceful nature.