This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Social & Preventive Medicine
[{'content': 'Pack year means \nSelect and explain. \nA. 10 cigarettes per day for 1 year, B. 20 cigarettes per day for 1 year, C. 40 cigarettes per day for 1 year, D. 50 cigarettes per day for 1 year', 'role': 'user'}, {'content': 'Answer: B \nExplanation: (B) 20 cigarettes per day for 1 year# A pack-year is a quantification of cigarette smoking.> 1 pack-year is equal to smoking 20 cigarettes (1 pack) per day for 1 year, or 40 cigarettes per day for half a year, and so on.> Number of pack-years = (packs smoked per day) * (years as a smoker).', 'role': 'assistant'}]