This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anatomy
What is the percentage of immunoglobulins present in proteins? 
Select and explain. 
A. 5%, B. 10%, C. 15%, D. 20%
D: 20%
Answer: D: 20% 
Explanation: Immunoglobulins constitute 20 to 25% of total serum proteins. Based on physiochemical and antigenic differences, five classes of immunoglobulins have been recognized: IgG, IgA, IgM, IgD, and IgE.(Ref: Ananthanarayan 9th edition, p93)