This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Indicators of Health, Subject name: Social & Preventive Medicine
[{'content': "Expectation of life, free of disability is known as: \nSelect and explain. \nA. Park's index, B. Smith's index, C. Sullivan's index, D. Life index", 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. (c) Sullivan's index* Sullivan's Index = Life Expectancy MINUS Duration of disability (bed disability and inability to perform major activities)- It is one of the most advanced indicators currently available", 'role': 'assistant'}]