Earlier We Discussed the Concept of Isostasy,where Lower Density Rocks

Earlier we discussed the concept of isostasy,where lower density rocks rise higher than higher density rocks.How is the variation of water depth at spreading centers (ridges) controlled by isostasy?

A) Volcanic rocks are lighter than other rocks,and so the abundant volcanic rocks at the ridges are lower density features that produce the seafloor topography.
B) It has nothing to do with isostasy; the areas are simply high because there are chains of active volcanos along the ridge crest,producing the topography.
C) Oceanic ridges are sites where the lithosphere is carried into the mantle on one side (aka subduction zones) ,and the volcanos along these margins produce the ridge by buildup of lower density crust.
D) The lithosphere cools as it moves away from the ridge axis by sea floor spreading,and cooler rocks are lower density,so the sea floor gets deeper as the lithosphere gets more dense.