Why Is the Thickness of Ooze Along the Ocean Floor

Why is the thickness of ooze along the ocean floor not always an accurate indication of the biological productivity of surface water in a given area?

A) Beyond certain depths, both calcareous and siliceous ooze will tend to dissolve in the water.
B) Animal remains tend to get eaten in the upper layers and therefore will never fall to the bottom.
C) Marine life generally migrate and don't stay in any one place that long.
D) Currents take most of the material away.