During the past year, a 34-year-old woman has had palpitations, fatigue, and worsening chest pain. On physicalexamination, she is afebrile. Her pulse is 75/min, respirations are 15/min, and blood pressure is 110/70 mm Hg. Auscultation of the chest indicates a midsystolic click with late systolic murmur. A review of systems indicates that the patient has one or two anxiety attacks per month. An echocardiogram is most likely to show which of the following? (A) Aortic valvular vegetations (B) Pulmonic stenosis (C) Mitral valve prolapse (D) Patent ductus arteriosus (E) Tricuspid valve regurgitation