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
The organism most commonly implicated in the causation of subacute bacterial endocarditis is: 
Select and explain. 
A. S. albus, B. S. Aureus, C. S. typhi, D. S. Viridans
D: S. Viridans
Answer: D: S. Viridans 
Explanation: None