What is the main function of the cell membrane in all cells

Regulate the movement of materials in and out of the cell

Explanation:

The cell membrane of animal cells is a thin membrane that lines the entire cell surface, and it is a selectively permeable membrane, thus, allowing the entry of useful materials into the cell and exit of waste products out of the cell.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."