"At that time, there happened great disturbances among the lower ranks of people, by which England was nearly ruined. Never was a country in such jeopardy, and all because some commoners sought to claim liberties to which they were not entitled. It is customary in England, as in other countries, for the nobility to have great privileges over the commoners, who are bound by law and custom to plow the lands of nobles, to harvest the grain, to carry it home to the barn, and to perform various other services for their lords. The evil-disposed in these districts began to rise, saying they were too severely oppressed; that at the beginning of the world there were no unfree people, and that no one ought to be treated as such, unless he had committed treason against his lord, as Lucifer had done against God: but they had done no such thing, for they were men formed after the same likeness as their lords, who treated them like beasts. They could no longer bear this, but had determined to be free. And if they were to do any work for their lords, they demanded to be paid for it." Jean Froissart, French chronicler, late 1300s English nobles resisted peasant demands such as those described in the passage because agricultural labor in many parts of fourteenth-century Afro-Eurasia had become scarce as a result of which of the following developments?
a. Slavery
b. Child labor
c. Trafficking
d. Serfdom