Conrad and Meyer (1958) found evidence to support the claim that the annual rates of return to slave agriculture were

(a) high enough to attract investment funds away from other alternatives in the cotton South.
(b) high enough to benefit the entire Southern economy through the profits generated and the backward and forward links to other businesses.
(c) relatively low in the new frontier, thus encouraging the new cotton producing areas of the South to move away from the slave system.
(d) low enough that the people in the North could purchase the slaves and free them at minimal cost.

(a)