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: Medicine
[{'content': 'Commonest congenital heart disease is: \nSelect and explain. \nA. Mitral valve prolapse, B. Atrial septal defect, C. Ventricular septal defect, D. Persistent ductus arteriosus', 'role': 'user'}, {'content': 'Answer: C \nExplanation: VSD is the most common congenital cardiac defect.', 'role': 'assistant'}]