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 antibody has maximum concentration in GI secretions 
Select and explain. 
A. IgG, B. IgM, C. IgA, D. IgD
C: IgA
Answer: C: IgA 
Explanation: IgA antibody

It is the second most abundant antibody (after IgG).
It is major immunoglubulin in clostrum, saliva, tears, respiratory and gastrointestinal secretions.
IgA occurs in two forms.