The correct answer is - D. Volcanic mountains form on land but not on the ocean floor.
The volcanic mountains are a result of the volcanic activity. They appear at places where there's a plate boundary, most often in the places where there's a subduction zone.
These mountains can only form on the land or above the surface of the water, but not on the ocean floor. The reason why they can not form on the ocean floor is because the magma is cooling down almost instantly, and it is pretty much impossible for a volcanic mountain to form. On the other hand, they can be found totally submerged in water, but those are volcanic mountains that have formed on land, got eroded, and sunk bellow the water.
