Which type of cell does not contain a nucleus enabling it to carry more hemoglobin? leucocyte white blood cell nerve cell erythrocyte

Erythrocytes also called as red blood cells. These are the cells which does not possess nucleus. They exhibit a pigment named as hemoglobin, the heme  component of the hemoglobin has affinity for oxygen. It carries oxygen to all the parts of the body.

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

that is true   : ) hope this you