An Infant Is Born with Blood Type AB

An infant is born with blood type AB. The father is type A and the mother is type B. The father asks why the baby has a blood type different from that of the parents. The nurse's answer should be based on the knowledge that which is true?

A) Both A and B blood types are dominant.
B) Types A and B are recessive when linked together.
C) The baby has a mutation of the parents' blood types.
D) Type A is recessive and links more easily with type B.