Lagoons used for purification of polluted water_______________?

A. Are large shallow artificial lakes also known as clarification lakes, maturation ponds or
oxidation ponds
B. Use micro-organisms/bacteria in presence of dissolved oxygen
C. Gives an excellent final effluent (with 3 to 4 lagoons arranged in series) having suspended
solid < 1 mg/litre and BOD = 3.8 mg/litre
D. All A., B. & C.