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
ABO antibodies are 
Select and explain. 
A. IgG, B. IgA, C. IgM, D. IgD
C: IgM
Answer: C: IgM 
Explanation: Antibody of ABO, Rh system is IgM.