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: Medicine
[{'content': 'Cerebral Ischemia occur when cerebral blood flow is less than - \nSelect and explain. \nA. 10 ml/100g/minute, B. 20 ml/100g/minute, C. 40 ml/100g/minute, D. 50 ml/100g/minute', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]