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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 be called as highly polluted with organic wastes, are

1. A and B
2. A and D
3. B and C
4. B and D

Correct answer: B and C

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