Answer:
Seafloor spreading occurs at Feature A and subduction occurs at Feature B
Explanation:
On the image we can see two contrasting features. One of them gives rise to the new crust, while the other destroys the old one. Feature A is a mid-ocean ridge. This is the place where there's a divergent plate boundary. The gap left behind the plates that move away is filled with magma, which constantly piles up new layers that are becoming new crust. It is hear where the ocean floor is spreading. Feature B is the opposite, it is a subduction zone. In the subduction zones, one of the plates moves below the other plate, reaching the mantle layer, getting melted and destroyed. On the place of the boundary, there's a deep valley that forms in the gap, known as an ocean trench.