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': 'Strength of chlorine to kill cyclops is – \nSelect and explain. \nA. 1 ppm, B. 2 ppm, C. 5 ppm, D. 10 ppm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]