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': 'Which one of the following cardiac lesions is at highest risk of occurrence of infective endocarditis \nSelect and explain. \nA. Atrial septal defect, B. Mitral valve prolapse without regurgitation, C. Valvular aortic regurgitation, D. Mitral stenosis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]