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: Microbiology
Which factor of S.Aureus is responsible for Coagglutination reaction? 
Select and explain. 
A. Protein-A, B. Clumping factor, C. Hemolysin, D. Techoic acid
A: Protein-A
Answer: A: Protein-A 
Explanation: Protein-A binds to Fc region of IgG leaving Fab region free to bind to an antigen, forming the basis of coagglutination reaction.