Final answer:
The most common cause of mitral regurgitation in elderly patients is calcified mitral annulus.
Step-by-step explanation:
The most common cause of mitral regurgitation in elderly patients is c) Calcified mitral annulus.
Calcified mitral annulus refers to the hardening and narrowing of the ring around the mitral valve. This can restrict the proper closure of the valve, causing blood to flow backward into the left atrium.
Other causes of mitral regurgitation include papillary muscle dysfunction (d), atrial fibrillation (a), and rheumatic heart disease (b).