Answer is D. sea floor spreading
Sea floor spreading is a process which takes place at mid-ocean ridges. The ridges are the boundaries between two plates which are moving away from each other. When the plates get separated after moving apart, the crust is stressed and weakened. As a result magma comes out from under the surface by breaking the crust and magma creates new sea floor. The plates move apart, carrying the “new” sea floor with it. At first, sea floor spreading was not proven. But magnetic reversal proves seafloor spreading because the polarity of the Earth’s magnetic field in rocks.
