A man with blood group 'A' marries with blood group 'B'. what are all the possible blood groups of their offsprings?

The correct option is D A,B, AB and O

Blood groups are inherited from our biological parents in the same way as eye color and other genetic traits. Within the ABO Blood Group system:-

the A and B genes are co-dominant, i.e. these will be expressed whenever the gene is present.

The O gene is silent and only expressed when neither A nor B is present.

This is then is solved by punnet square method. If a man with blood group A marry a woman with blood group B then there are 4 possibilities:-

AO

BO

Ab

O

So the correct option is ' A, B, AB, and O'.