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
Not a pa of firearm: NEET 13 
Select and explain. 
A. Bolt, B. Piston, C. Extractor, D. Muzzle
B: Piston
Answer: B: Piston 
Explanation: Ans. Piston