This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Social & Preventive Medicine
Biological oxidation demand is determined by 
Select and explain. 
A. Sullage, B. Suspended Solids, C. Algae in water, D. Organic matter
D: Organic matter
Answer: D: Organic matter 
Explanation: (D) Organic matter # Biochemical oxygen demand (BOD) is the amount of oxygen absorbed by a sample of sewage during a specified period at a specified temperature for the aerobic destruction or use of organic matter by living organisms. BOD > 300 mg/L is 'strong' sewage; BOD < 100 mg/L is 'weak' sewage. It is due to organic matter present in the sewage.