Why did spanish leaders want to push spanish control into north america in the mid-1500's?

They wanted to push in North America because they knew that by gaining control over this continent or at least parts of it would mean a lot to the spanish crown and would also be rewared. 

Ibelieve the answer is c

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.