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 immunoglobulin is scarce in human serum 
Select and explain. 
A. IgA, B. IgG, C. IgM, D. IgE
D: IgE
Answer: D: IgE 
Explanation: Antibody with least serum concentration IgE(0.0004)