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: Pathology
Father’s blood group is ‘A’ & mother’s blood group is ‘AB'. Which of the following blood group is not possible in any of their children? 
Select and explain. 
A. A, B. B, C. O, D. AB
C: O
Answer: C: O 
Explanation: None