This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
[{'content': 'Fixed-splitting of S2 is seen in \nSelect and explain. \nA. ASD, B. MS, C. PDA, D. PR', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A fixed split S2 indicates an atrial septal defect (ASD). Spitting at both expiratory and inspiratory phases but does NOT lengthen with inspiration Compared to Wide splitting where there is splitting during expiration and even wider during inspiration, which is seen in conditions with delayed conduction down the right bundle ref - Harrisons internal medicine 20e pg 1671, 1672f', 'role': 'assistant'}]