This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
[{'content': 'Definition of TIA is, patient signs and symptoms resolve by \nSelect and explain. \nA. 24 hours, B. 36 hours, C. 48 hours, D. 72 hours', 'role': 'user'}, {'content': "Answer: A \nExplanation: When blood flow is quickly restored, brain tissue can recover fully and the patient's symptoms are only transient, this is called a transient ischemic attack (TIA). The definition of TIA requires that all neurologic signs and symptoms resolve within 24 h without evidence of brain infarction on brain imaging. Most TIAs last <1 h.Stroke has occurred if the neurologic signs and symptoms last for >24 h or brain infarction is demonstratedRef: Harrison 19e pg: 2559", 'role': 'assistant'}]