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
Most common cause and the most common valve affected in Infective endocarditis in I.V drug abusers 
Select and explain. 
A. Streptococcus viridans—tricuspid valve, B. Pseudomonas—mitral valve, C. Staphylococcus aureus—tricuspid valve, D. Streptococcus bovis—mitral valve
C: Staphylococcus aureus—tricuspid valve
Answer: C: Staphylococcus aureus—tricuspid valve 
Explanation: In I.V drug abusers it is staph.aureus to cause Infective endocarditis most commonly and the right sided valves are more commonly affected than the left sided valves