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': 'Paradoxical splitting of S 2 is seen in ? \nSelect and explain. \nA. ASD, B. Mitral stenosis, C. Severe pulmonary stenosis, D. Severe aoic stenosis', 'role': 'user'}, {'content': 'Answer: D \nExplanation: As AS increases in severity, LV systole may become prolonged so that the aoic valve closure sound no longer precedes the pulmonic valve closure sound, and the two components may become synchronous, or aoic valve closure may even follow pulmonic valve closure, causing paradoxical splitting of S 2 ( Harrison&;s principle of internal medicine,18th edition,pg no. 1939)', 'role': 'assistant'}]