Final answer:
The offspring could have any of the four possible ABO blood types: A, AB, B, and O.
Step-by-step explanation:
In this case, the father has blood type A (genotype AO) and the mother has blood type B (genotype BO). According to the ABO inheritance chart, this mating type can produce children with any of the four possible ABO blood types: A, AB, B, and O. Therefore, the offspring of these biological parents could have any of these blood types.