Why Do Slash-And-Burn Cultivators Stop Using a Plot of Land

Why do slash-and-burn cultivators stop using a plot of land every two to three years?

A) They burn so much wood that the air becomes too polluted to support a healthful existence.
B) Slash-and-burn cultivation is unique to segmentary-lineage organized societies, and crop rotation follows the cycle of interlineage exchange.
C) Slash-and-burn cultivation is associated with big-game hunting, which requires regular movement so as not to deplete the animal population.
D) Slash-and-burn cultivators use relatively primitive irrigation systems, which have to be repaired every three to four years.
E) They do not use fertilizer; thus, their crops exhaust the soil quickly.