Final answer:
The spread of the bubonic plague across Eurasia was most responsible due to infected rats spreading the disease through fleas on their bodies
Step-by-step explanation:
The most responsible factor for the spread of the bubonic plague across Eurasia was rats. These rodents carried infected fleas which transmitted the plague bacterium, Yersinia pestis, to humans. When infected rats and fleas came into contact with humans, usually in crowded urban areas, the disease spread rapidly. Sailors and traders inadvertently helped facilitate the spread of the disease as they unknowingly transported rats on their ships.
Learn more about the spread of the bubonic plague across Eurasia