This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Health Education & Health Planning, Subject name: Social & Preventive Medicine
[{'content': 'BMI obesity starts: \nSelect and explain. \nA. 25, B. 30, C. 35, D. 40', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. (b)~30Ref : K. Park 23rd ed. / 399-400* BMI is Body Mass Index, aka Quetlets Index.* It is calculated as: BMI = weight (kg)/height (m)2ClassificationBMIUnderweight<18.5Normal BMI18.5-24.99Overweight/pre-obese25-29.99Obesity>30.0* Grade I* Grade II* Grade III* 30-35* 35-40* >50', 'role': 'assistant'}]