The "limestone" is supported by the rock cycle.
(1) they keep toxic substances out of the cell;
(2) they contain receptors and channels that allow specific molecules, such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the cell and the outside environment;
(3) they separate vital but incompatible metabolic processes conducted within organelles.
There are a couple reasons the ice is important to polar bears, but given the choices you have the correct one would be:
A. The polar bears can’t out swim the seals, so they sit quietly on an ice platform and attack the seals when they come up for air.
