Answer:
B.sea floor spreading
Step-by-step explanation:
The creation of new crusts at the middle of the mid- ocean ridges is also sea floor spreading.
The process of sea floor spreading entails the creation of new crusts at the margin of the oceanic crusts.
Basaltic materials from the subsurface upwells to the surface.
They cool and solidifies to form new crusts. The old crust is moved behind and away from the margin. This way, sea floor is formed and it spreads in like manner.
At this margin sea floor is created and at a convergent margin, it is destroyed.