Which of the following cardiac valve abnormalities occurs most frequently in young women?
A. Aortic stenosis caused by calcification of the aortic valve
B. Mitral stenosis caused by scarring resulting from a previous episode of acute rheumatic fever
C. Mitral valve prolapse
D. Aortic valve incompetence (aortic insufficiency) caused by previous rheumatic fever
E. Idiopathic hypertrophic subaortic stenosis (IHHS)