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
Lining of open sanitary well should be extended to a minimum depth of? 
Select and explain. 
A. 5 feet, B. 10 feet, C. 15 feet, D. 20 feet
D: 20 feet
Answer: D: 20 feet 
Explanation: Ans. is 'd' i.e.,20 feet the well should be located not less than 15 m (50 feet) from likely sources of contamination. The well should be located at a higher elevation with rspect to a possible source of contamination.