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
Sullivan's index measures - 
Select and explain. 
A. Moality, B. Morbidty, C. Infectivity, D. Disability
D: Disability
Answer: D: Disability 
Explanation: Ans. is 'd' i.e., Disability