Why did enslavers begin "selling down the river?"

Select the best answer from the choices provided.
A.
Enslavers in the deep South paid more money for enslaved workers.
B.
Enslavers did not have to face a penalty for selling enslaved workers in the South.
C.
Most enslaved workers wanted to move to the South because of the better conditions.
D.
Northern enslavers were losing money by keeping their enslaved workers.