If both husband and wife have blood group A, then their child cannot have which of the following blood group?

a) A
b) O
c) AB
d) None

Ans- [C]

Explanation-

Blood Group	Antigen
A	Has only A antigen on red cells (and B antibody in the plasma)
B	Has only B antigen on red cells (and A antibody in the plasma)
AB	Has both A and B antigens on red cells (but neither A nor B antibody in the plasma)
O	Has neither A nor B antigens on red cells (but both A and B antibody are in the plasma)

Blood group is determined by the antigen present on RBC. As you can see, blood group A has only antigen A on RBCs. Therefore, baby of both the parents will either have antigen A on its blood cells or no antigen on it because antigen B is absent in both the parents.

Thus, either it will have blood group A or O. It can not have blood group B or AB.