a. carbon

b. sulphur

c. calcium

d. phosphorus

Answer: d. phosphorus

Explanation: Phosphorus in the form of phosphates and nitrates acts as nutrients that creates flowering. The increasing growth of algae due to these pollutants added to water bodies through human activities is called cultural eutrophication. This, in turn, compresses the body of water and leads to the death of living things. The decay of this algae and the dead aquatic organisms, further degrades the dissolved oxygen content in the water.