Research by Fogel and Engerman shows that, holding other factors constant, output per unit of total input was highest for Southern farms with: a. no slaves. b. 1 to 15 slaves. c. 16 to 50 slaves. d. 50 or more slaves.

D. 50 or more slaves

Explanation:

Engerman and Fogel argued that economic incentives of owners and slaves were central to the way slavery functioned.They found that by the approach of the Civil War in 1860, the system had never been stronger economically. Slaves were selling at record high prices, and slave owners enjoyed substantial profits, especially on the larger plantations. Engerman and Fogel showed that, although violence or the threat of violence was part of the life of a slave, positive incentives in the form of better material conditions and even cash payments led to a slave labor force that was highly motivated. Through the statistical analysis of farm data, they also showed that productivity levels were higher than on free farms, especially so on plantations, where cotton was produced using gang labor.

the answer is b: a lockout