This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Medicine
[{'content': 'Cerebral Ischemia occurs 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: *Acute occlusion of an intracranial vessel causes a reduction in blood flow to the brain region it supplies*Cerebral blood flow to zero causes death of brain tissue within 4-10 minutes*<16-18 mL/100 g tissue per minute cause infarction within an hour; * <20 mL/100 g tissue per minute cause ischemia without infarction unless prolonged for several hours or days.*If blood flow is restored prior to a significant amount of cell death, the patient may experience only TIA.*Tissue surrounding the core region of infarction is ischemic but reversibly dysfunctional and is referred to as the ischemic penumbra. *The ischemic penumbra will eventually infarct if no change in flow occurs.(Ref: Harrison's 18/e p3271 )", 'role': 'assistant'}]