This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Water, Subject name: Social & Preventive Medicine
[{'content': 'Minimum contact period for chlorination - \nSelect and explain. \nA. 30 minutes, B. 1 hour, C. 2 hours, D. 5 hour', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., 1 hour Water typeRecommendedResidual chlorine levelContact periodDrinking waterWater bodies, post disasterSwimming pool sanitation> 0.5 mg per litre (ppm) >0.7 mg per litre (ppm)> 1.0 mg per litre (ppm)1 hour1 hour1 hour", 'role': 'assistant'}]