How did John D. Rockefeller horizontally integrate his monopoly in 1880? A.)He purchased iron mines around the country to add to his business.
B.)He created a trust that controlled ninety percent of the nation's oil refineries.
C.)He created a trust that controlled oil wells, refineries, and distribution networks.
D.)He purchased coal plants around the country to add to his business.

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.