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
The Ig found in exocrine secretions is: 
Select and explain. 
A. IgG, B. IgD, C. IgM, D. IgA
D: IgA
Answer: D: IgA 
Explanation: None