Concept:The donor red blood cells must not be attacked by antibodies present in the recipient's plasma.Explanation:The father has blood group AB, so his red blood cells carry both A and B antigens.For the transfusion to be successful, the sick baby's plasma must not contain antibodies against these antigens.Blood group A has anti-B antibodies; blood group B has anti-A antibodies; blood group O has both.Only blood group AB has neither anti-A nor anti-B antibodies.Therefore, the baby can safely receive AB blood only if the baby also belongs to blood group AB.Answer:C. AB