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': 'Above which level of heat stress index it is not possible to work comfortably – \nSelect and explain. \nA. 20 – 40, B. 40 – 60, C. 60 – 80, D. 80 – 100', 'role': 'user'}, {'content': 'Answer: B \nExplanation: HSI 40-60 causes severe heat strain and it is not possible to work comfortably.', 'role': 'assistant'}]