This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Local and Regional Anesthesia), Subject name: Anaesthesia
[{'content': "Concentration of Local anesthetic agent used for Bier's block is \nSelect and explain. \nA. 0.50%, B. 1-2%, C. 4%, D. 5%", 'role': 'user'}, {'content': "Answer: A \nExplanation: 0.5% (Bier's block: Intravenous regional anesthesia)", 'role': 'assistant'}]