21. Holden read the following statement, "As the continental plates spread apart, new crust is created at a rate of about 4 centimeters per year." Which process directly contributes to the phenomenon described here?
A. Liquid magma from the mantle rises to the surface.
B. Tiny rock fragments are compressed to form new rock.
C. Crustal materials are eroded, and fragments are washed away.
D. Shock waves are created when two tectonic plates move past one another.