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
[{'content': 'Lining of open sanitary well should be extended to a minimum depth of? \nSelect and explain. \nA. 5 feet, B. 10 feet, C. 15 feet, D. 20 feet', 'role': 'user'}, {'content': "Answer: D \nExplanation: 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.", 'role': 'assistant'}]