The correct option is A unsanitary conditions.
Filth was a fact of life for all classes in the Middle Ages. Towns and cities were filthy, the streets open sewers; there was no running water and knowledge of hygiene was non-existent. Dung, garbage and animal carcasses were thrown into rivers and ditches, poisoning the water and the neighbouring areas. Fleas, rats, and mice flourished in these conditions. Indeed this was the perfect environment for the spread of infectious disease and plague: the Black Death was to kill over half of England’s population between 1348 and 1350. In the slum areas of cities, diseases like cholera, typhus, and diphtheria were endemic. Some could be linked to poor sanitation (cholera) and poor housing (TB) while others were spread by body lice (typhus). In addition, there were new industrial diseases. Hence, Option A is correct. Among the rest, the poison was not put in the water of community wells, people used herbal medicines due to lack of progression in science, and family members cared for the sick. Hence, these are incorrect.