The correct answer is (B) Highly Polluted
Biological Oxygen Demand (BOD) measures the oxygen used by microorganism to decompose the waste. Nitrates and phosphates contribute to a high level of BOD.
The river, which has a high level of BOD, indicates increased pollution in the river as the dissolved oxygen available in the water is being used by the microbes, resulting in a lesser oxygen level available to fish and other aquatic organisms.
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