Ocean Spreading Centers Are Highlands on the Ocean Floor, Sometimes

Ocean spreading centers are highlands on the ocean floor, sometimes referred to as submarine mountains. Oceanic crust worldwide is about the same thickness so isostasy would suggest the ocean floor should be as flat as Kansas. Which of the following statements best describes the origin of these submarine mountains?

A) Compression at the ridges produce local uplift along the ridge axis.
B) The ridges represent upwelling zones from the core which produces a bulge at the earth's surface.
C) The ridges are sites of young volcanoes that produce high topography on the sea floor, like Hawaii.
D) The mantle beneath the ridges remains hot for millions of years producing an elevated region along the ridge axis because hot rocks are lower density than cold rocks.