Final answer:
The most likely diagnosis is aortic valve stenosis based on the given information, which includes an M-mode echocardiogram, physical examination findings, and characteristic heart sounds.
Step-by-step explanation:
The most likely diagnosis based on the given information is B. Stenosis of the aortic valve. The M-mode echocardiogram showing multiple echoes within the aortic root suggests the presence of valve calcification or thickening. The aortic valve excursion of 7mm also indicates restricted valve opening, which is consistent with aortic valve stenosis. Additionally, the presence of a crescendo-decrescendo systolic ejection murmur (typical of aortic stenosis) and a diastolic decrescendo murmur (typical of aortic insufficiency) further supports the diagnosis of aortic valve stenosis.