The correct answer is: Bio-Chemical Oxygen Demand (B.O.D.)
Biochemical oxygen demand (BOD) is the amount of oxygen required by aerobic biological organisms to decompose organic matter present in a given water sample at a specified temperature over a specified time period. It is a measure of the organic pollution in water.
Dissolved oxygen (DO) is the amount of oxygen that is dissolved in water. It is essential for aquatic life, as it is used in respiration. DO levels can be affected by factors such as temperature, salinity, and pollution.
Chemical oxygen demand (COD) is a measure of the amount of oxygen required to oxidize all of the organic matter in a water sample. It is a more comprehensive measure of pollution than BOD, but it is also more difficult to measure.
None of these is the correct answer.