Answer:
it is:
overcrowded and unsanitary cityies- lets face it, cities are not sanitary in the least
trade ships bring infected passengers and rats-really? is it a good idea to bring a bunvh of people over during a plague?
fleas infested rats- our best theory as to how the plague even started, was with infected bacterium Yersinia pestis. The disease was likely transmitted from rodents to humans by the bite of infected fleas.
Step-by-step explanation: