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': "Cause of Farmer's lung – \nSelect and explain. \nA. Cotton dust, B. Grain dust, C. Sugarcane dust, D. Iron", 'role': 'user'}, {'content': "Answer: B \nExplanation: Farmer's lung is caused by Hay or grain dust.", 'role': 'assistant'}]