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': "Sullivan's Index is \nSelect and explain. \nA. Disability Free Life expectancy(DFLE), B. Disability Adjusted Life expectancy(DALE), C. Quality Adjusted Life Expectancy(QALE), D. Health Adjusted Life Expectancy(HALE)", 'role': 'user'}, {'content': "Answer: A \nExplanation: Sullivan's Index : Life expectancy - Duration of disability.", 'role': 'assistant'}]