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': 'In a town of population 5000, 500 are already myopic on January 1, 2011. The number of new myopia cases is 90 till it December 31, 2011. Calculate the incidence of Myopia in the town in 2011- \nSelect and explain. \nA. 0.018, B. 0.02, C. 0.05, D. 18', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Out of 5000, 500 are already myopic. Thus, population at risk in the question = 5000 - 500 = 4500\n\nIncidence =\xa0New cases in the year / Population at risk in the year = 90 / 4500\xa0= 0.02', 'role': 'assistant'}]