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: Forensic Medicine
[{'content': 'Not a part of a firearm - \nSelect and explain. \nA. Bolt, B. Piston, C. Extractor, D. Muzzle', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Parts of firearm weapon are:-\n\n\nBarrel: Which has two ends: breech end and muzzle (breech end may have a chamber and an extractor).\nAction: Consists of\n\n(a) breechblock (bolt),\n(b) firing pin or striker pin or hammer,\n(c) trigger.\n\nGrip (buttstock and magazine.', 'role': 'assistant'}]