What Was a Factor Responsible for the Spread of Disease

What was a factor responsible for the spread of disease in the Middle Ages?

A) Hospitals served as resting places for travelers as well as places for sick people to be treated and recuperate.
B) Hospitals had special aeration systems that spread germs throughout the building.
C) Hospitals did not allow sick people to enter for treatment; since they were outside the building, they spread their germs more easily.
D) Hospitals required that sick people roam about the countryside because physicians of the time believed that exercise was beneficial.