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
Agglutination with 'O' antigen of S. typhi is inhibited by - 
Select and explain. 
A. Vi antigen, B. Pili antigen, C. Flagellar antigen, D. All of the above
A: Vi antigen
Answer: A: Vi antigen 
Explanation: None