The nucleolus the nucleolus is a dark-staining spherical body found within the mitochondria is the primary site of protein synthesis is the site of ribosome assembly in a cell is the site of lipid production in a cell

The primary site for ribosome assembly

Explanation:

The nucleolus is a dark-staining spherical body, but it is found within the nucleus, not in the mitochondria. New ribosomes are assembled in the nucleolus, specifically the subunits of the rRNA or the ribosomal RNA. It is the biggest structure within the nucleus and can be seen during interphase. Interestingly, studies have shown that the size of the nucleolus can determine the life span of the cell.

✿   this landform has a high elevation and a high relief

✿   this landform is a mountain

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