A Child Has Been Diagnosed with Sickle-Cell Disease

A child has been diagnosed with sickle-cell disease. Both parents deny having the disease themselves. The parents ask the nurse how their child got this disease. The nurse recognizes that the only possible explanation of the etiology is:

A) The father is not the biological father of the infant.
B) The mother of the child has the trait, but the father doesn't.
C) The father of the child has the trait, but the mother doesn't.
D) The mother and the father of the child have the sickle-cell trait.