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': 'Following are true regarding chlorination except – \nSelect and explain. \nA. Residual chlorine is 0.5 mg/lit., B. Contact period – 30 minute, C. Water should not be turbid, D. Chlorine demand should be estimated', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Contact period of 1 hour is recommended.', 'role': 'assistant'}]