Answer:
the answer is: b. impact of the plague on population
Step-by-step explanation:
At that time, the European still hasn't undergone enough advancement in medical science to handle the plague. Because of this, Regardless of their massive wealth and influence, Byzantine empire still lost a large number of citizens in productive age due to the plague. This massively weakened the empire both economically and in terms of military power. Eventual, that all lead to its fall.