The Pandemic Known as Justinian's Plague Spread Rapidly Through the Eastern

The pandemic known as Justinian's plague spread rapidly through the eastern and western part of the Roman Empire because it:

A) was a very virulent strain of smallpox.
B) was carried by birds who migrated great distances.
C) traveled along well-established trade routes both within and outside the empire.
D) had a very long incubation period,which meant people could travel long distances without knowing they were infecting people.
E) was exacerbated by an epidemic of influenza in the empire.