This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Immunoglobulin secreted by fetus as primary response - 
Select and explain. 
A. IgA, B. IgM, C. IgG, D. IgD
B: IgM
Answer: B: IgM 
Explanation: Ans. is 'b' i.e., IgM