Explanation:
Blood group inheritance follows a specific pattern, and understanding this pattern can help determine the possible blood types of offspring.

Blood Group Inheritance:
- Blood group is determined by the presence or absence of specific antigens on the surface of red blood cells.
- There are four main blood groups: A, B, AB, and O.
- These blood groups are determined by the presence or absence of two antigens, A and B.
- The blood group is also determined by the presence or absence of a third antigen called the Rh factor, which can be either positive (+) or negative (-).

Blood Group A:
- A person with blood group A has antigen A on the surface of their red blood cells.
- They can have two possible genotypes: AA or AO.
- AA indicates homozygosity, meaning both alleles are the same (A).

Blood Group AB:
- A person with blood group AB has both antigens A and B on the surface of their red blood cells.
- They can only have one possible genotype: AB.
- AB indicates heterozygosity, meaning both alleles are different (A and B).

Blood Group B:
- A person with blood group B has antigen B on the surface of their red blood cells.
- They can have two possible genotypes: BB or BO.
- BB indicates homozygosity, meaning both alleles are the same (B).

Blood Group O:
- A person with blood group O does not have either antigen A or B on the surface of their red blood cells.
- They can only have one possible genotype: OO.
- OO indicates homozygosity, meaning both alleles are the same (O).

Marriage Between Blood Group A and AB:
- When a man with blood group A (genotype AO) marries a woman with blood group AB (genotype AB), their possible offspring's blood types can be determined by considering the possible combinations of alleles.
- The man's possible alleles are A and O, while the woman's possible alleles are A and B.
- The possible combinations of alleles for the offspring are AA, AB, AO, and BO.

Identifying the Man's Homozygosity:
- If the man is homozygous (genotype AA), all his possible offspring's blood types would be A (genotypes AA, AB, and AO).
- However, if any of the offspring's blood types are B (genotype BO), it indicates that the man is not homozygous.
- Therefore, the presence of blood type B among the progeny (option B) indicates that the man is not homozygous.