Which of the following is the most common cause of subacute endocarditis?: (A) Staphylococcus aureus, (B) Staphylococcus epidermidis, (C) Streptococcus viridans, (D) Streptococcus pyogenes
Answer is C. Intraoral Streptococcus viridans is the most common cause of subacute endocarditis. 
Staphylococcus aureus is the most common cause of acute endocarditis.