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: Anaesthesia
A 25 yr old male is undergoing incision and drainage of abscess under general anaesthesia with spontaneous respiration. The most efficient anaesthetic circuit is: 
Select and explain. 
A. Mapleson A, B. Mapleson B, C. Mapleson C, D. Mapleson D
A: Mapleson A
Answer: A: Mapleson A 
Explanation: Mapleson A Breathing circuits A. Open system (Out dated) B. Semiopen (Out dated) C. Semiclosed (Mapleson circuits) D. Closed