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 is true about Widal reaction - 
Select and explain. 
A. Antibody to H Ag appears first and persists, B. Antibody to 0 Ag appears first and persists, C. Antibodies to H & 0 Ag appears simultaneously and persists, D. None of the above
A: Antibody to H Ag appears first and persists
Answer: A: Antibody to H Ag appears first and persists 
Explanation: Ans. is 'a' i.e., Antibody to 'H' antigen appears first and persists