The measured BOD values for four different water samples (A-D) are as follows: A =3 ppm; B =18 ppm; C =21 ppm; D =4 ppm. The water samples which can…

The measured BOD values for four different water samples (A-D) are as follows: $\displaystyle \mathrm{A}=3 \mathrm{ppm} ; \mathrm{B}=18 \mathrm{ppm} ; \mathrm{C}=21 \mathrm{ppm} ; \mathrm{D}=4 \mathrm{ppm}$. The water samples which can be called as highly polluted with organic wastes, are