Answer:
Option A, cities were densely populated
Explanation:
Typhus is a disease caused by body lice. It spread like an epidemic disease when the city is overpopulated. Extreme overpopulation causes the transfer of lice from infected person's body to another person's body when they are nearby. This nearness ease the travelling of lice from body of one person to the body of another person .
High densities in city means the number of people living in a given area is very high. Thus, large number of people living in small area ease the spread of Typhus and other disease.
Hence, option A is correct
