Answer
d.
Work Step by Step
The man and woman could have children that have blood type A, B, AB, or O. The man with the type B blood could have either genotype BB or BO; therefore, he can contribute either a B or an O allele to his sperm cells. The woman with the type A blood could be either genotype AA or AO, meaning she can contribute eggs with either the A or O allele. So their children can have genotypes AO, AB, BO, or OO. The genotype AO gives rise to A blood, AB gives rise to AB blood, BO gives rise to B blood, and OO gives rise to O blood.
