This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuromuscular Blocker, Subject name: Anaesthesia
[{'content': 'First neuromuscular blocker to be used clinically:- \nSelect and explain. \nA. D-tubocurare, B. Succinylcholine, C. Doxacurium, D. Mivacurium', 'role': 'user'}, {'content': 'Answer: A \nExplanation: d-tubocurare is naturally occurring neuromuscular blocker and was first neuromuscular blocker to be used clinically. It is extract of curare plant. Not in clinical use since it release huge amount of histamine and has very long duration of action.', 'role': 'assistant'}]