This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Retina, Subject name: Ophthalmology
[{'content': 'Macular degeneration is caused by: \nSelect and explain. \nA. Chronic alcoholism, B. Smoking, C. Diabetes mellitus, D. Eales disease', 'role': 'user'}, {'content': 'Answer: B \nExplanation: b smoking refkhurana 3rd/e p. 282', 'role': 'assistant'}]