This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
The biological oxygen demand (BOD) indicates 
Select and explain. 
A. Organic matter, B. Bacterial content, C. Anaerobic bacteria, D. Chemicals
A: Organic matter
Answer: A: Organic matter 
Explanation: Biological Oxygen Demand (BOD): Is defined as ‘amount of oxygen absorbed by a sample of sewage’ during a specified period (Generally 5 days), at a specified temperature (generally 20° C) for aerobic destruction or use of organic matter by living organisms.
Strong Sewage has BOD > 300 g/litre and Weak Sewage has BOD < 100 g/litre.