They are asking us the possible blood types for a child of parents with AB blood type.
This means that both parents have one allele for antigen A (Iᵃ) and one allele for antigen B (IᵃIᵇ):
Mother: IᵃIᵇ
Father: IᵃIᵇ
Just from that, the child cannot be type O, because there is no allele for not having any antigen (i).
Let's look at the Punnet's square:
As we can see, the child of this couple could have blood type A, B, or AB.
This means the right answer is D. I, Il, and Ill
