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': "30 out of 50 smokers and 10 out of 50 non smokers develop lung cancer. What is odd's Ratio \nSelect and explain. \nA. 4, B. 2.8, C. 6, D. 7", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]