The Romans Were Able to Support Cities with Large Populations

The Romans were able to support cities with large populations due,in no small measure,to the:

A) efficient police departments that made the Roman cities safer than most villages.
B) well-trained fire brigades that made individual losses from fire very rare.
C) prevalence of a great many open-air restaurants that made feeding the large population easier.
D) construction of a system of aqueducts to allow a steady supply of potable water to the cities.
E) development of large hospitals to care for the general population.