A man with blood type A and a woman with blood type B have a child. If this child has type O blood, which of the following statements must be true?
A) The father could be homozygous A.
B) The mother has homozygous B blood type.
C) The maternal grandmother is homozygous A.
D) The paternal grandmother could have type O blood.
Answer: D) The paternal grandmother could have type O blood.