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': 'In a patient with ischaemic stroke, intravenous recombinant tissue plasminogenactivator has mainly been found to be useful during the initial - \nSelect and explain. \nA. 3 hours, B. 6 hours, C. 12 hours, D. 24 hours', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]