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
Concentration of Local anesthetic agent used for Bier's block is 
Select and explain. 
A. 0.50%, B. 1-2%, C. 4%, D. 5%
A: 0.50%
Answer: A: 0.50% 
Explanation: 0.5% (Bier's block: Intravenous regional anesthesia)