Why was the hiring of germanic mercenaries by western roman emperors a mistake?
a. regular roman army joined with the mercenaries to attack the eastern roman empire.
b. the germanics lacked loyalty to rome and sometimes bought against the empire.
c. the regular roman army rose up against them are mercenaries and killed many of them.
d. the germanics were poor soldiers who cannot handle roman weapons

"b. The Germanics lacked loyalty to Rome and sometimes bought against the empire" is the best option from the list, since the Germanic tribes had very little connection to Rome or its empire and were just interest in getting paid.

The constant presence of diseases or infectious agents within a given geographic area or population group. it may also refer to the usual prevalence of a given disease with such area or group. it includes holoendemic and hyperendemic diseases. a holoendemic disease is one for which a high prevalent level of infection begins early in life and affects most of the child population, leading to a state of equilibrium such that the adult population shows evidence of the disease much less commonly than do children (malaria in many communities is a holoendemic disease). a hyperendemic disease is one that is constantly present at a high incidence and/or prevalence rate and affects all groups equally. so probably family history.