This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology Pa 1 (Immune Response, Antigen-Antibody Reactions, Hypersensitivity, Structure of Immune System, Immunodeficiency Disorders), 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: IgG has maximum serum concentration (12 mg/mL) and IgE has minimum serum concentration (0.00004mg/mL).