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
An inexpensive and efficient method of sewage disposal for a small community is – 
Select and explain. 
A. River outfall, B. Oxidation pond, C. Trickling filter, D. Activated sludge
B: Oxidation pond
Answer: B: Oxidation pond 
Explanation: None