It's becasue human populations are concentrated in areas that are lacking proper resources.
Earth is composed of four main layers, starting with an inner core at the planet's center, enveloped by the outer core, mantle, and crust. The inner core is a solid sphere made of iron and nickel metals about 759 miles (1,221 kilometers) in radius.
source: nasa
I think it may be B, a borrowed language. The others don't seem right.