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