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: Dental
[{'content': 'The point at which the chlorine demand of water is met\nis termed \nSelect and explain. \nA. Break point, B. Back wash, C. Loss of head, D. Chlorine demand', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]