Answer:
B. Isostatic equilibrium
Step-by-step explanation:
Isostasy is a state of balance or equilibrium between the lithospheric plate and the underlying mantle, the asthenosphere.
Due to the weight of the lithosphere, part of it sinks into the plastic asthenosphere and settles to an equilibrium position. This is what causes changes and differences in elevation on the earth.
As with all natural processes, the earth in itself tries to achieve stability and equilibrium in all it parts. The crust and a portion of the mantle forms the brittle lithosphere. The lithosphere floats on the plastic mantle. Due to density contrast, portions of the lithosphere tends to sink into the mantle from time to time. The lithosphere reaches a point where it no longer sinks and establishes an equilibrium with the asthenosphere.
This isostatic adjustment that occurs within the earth is responsible for the changes in elevations from places to places.
When portions of the crust gets eroded, it becomes lighter and rises up. When materials are deposited in adjacent areas or glaciers forms, they add increasing weight to the crust and causes it to further settle within the asthenosphere.