Plate tectonic theory can be best described as

Im not sure what you mean but, Plate tectonics is the theory that the outer rigid layer of the earth (the lithosphere) is divided into a couple of dozen "plates" that move around across the earth's surface relative to each other, like slabs of ice on a lake. the theory can best be described as earth's natural process by which its lithospheric plates slowly move about because of movement in the asthenosphere. 

The earth's natural process by which its lithospheric plates slowly move about because of movement ( in the asthenosphere )

The correct answer should be brand c.