Which of the following was the main reason for the rapid settlement of the Great Plains (in the American West) during the late 1800s? A. Congress passed a law requiring all public lands to be sold at auction.
B. Native Americans sold most of their tribal lands directly to railroad companies.
C. Congress passed a law allowing people to claim public land and convert it to private property through homesteading.
D. Speculators bought large parcels of land and then built factory towns to attract new immigrants.

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.