This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cytogenetic Disorders, 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 child? 
Select and explain. 
A. A, B. B, C. AB, D. O
D: O
Answer: D: O 
Explanation: Ans. is 'd' i.e.,OBlood group inheritance by phenotypeBlood group (Parents)OABABOOO or AO or BA or BAO or AO or AO, A, B, or ABA,B orABBO or BO, A, B or ABO or BA, B or ABABA or BA, B or ABA, BorABA, B or AB