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': 'Guineaworm infestation is common in workers of: \nSelect and explain. \nA. Step wells, B. Ponds, C. Fields, D. Cotton mills', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Step wells', 'role': 'assistant'}]