Why did slave owners in the 1850s begin to sell their city slaves to the countryside? a….

Why did slave owners in the 1850s begin to sell their city slaves to the countryside?
a.
They thought that their slaves would benefit the free black population living in the countryside.
b.
They thought their slaves would be able to assist local government fend off Indian attacks in the countryside.
c.
They thought their slaves had too much independence, which negatively influenced the relation between master and slave.
d.
They thought that their slaves would have an easier life if they lived in the countryside rather than in an urban environment of crime.