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: Physiology
Persons having anti-A and anti-B isoagglutinins in their serum belong to which blood group 
Select and explain. 
A. A, B. B, C. AB, D. O
D: O
Answer: D: O 
Explanation: None