Which of the following describes the most important cause of the demographic changes associated with the Columbian Exchange?
A: The spread of New World diseases to Afro-Eurasia and environmental damage in the Americas
B: The introduction of New World food crops to Afro-Eurasia and the spread of epidemic diseases to the Americas
C: Environmental degradation in Afro-Eurasia and the spread of Afro-Eurasian food crops to the Americas
D: European settlement in the Americas and the forced migration of Native Americans to Afro-Eurasia