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 serum concentration of which of the following human Ig is maximum: 
Select and explain. 
A. IgG, B. IgA, C. IgM, D. IgD
A: IgG
Answer: A: IgG 
Explanation: IgG