Why Is a Layer of the Atmosphere Called the Homosphere

Why is a layer of the atmosphere called the homosphere?

A) That layer is the habitable sphere for humans (Homo sapiens) .
B) That term is used because scientists have been unable to determine its composition and assume it is homogeneous.
C) That layer is composed of a blend of gases that is nearly uniform throughout.
D) That layer contains only one gas,nitrogen.