ABO Blood Group Inheritance Rules Steps:

• Identify parental genotypes: A can be AA/AO, B as BB/BO, AB as AB, O as OO.
• Children inherit one allele from each parent; possible phenotypes must match combinations (e.g., A and O parents can produce A or O child).
• Trace lineage: Ensure no child has alleles absent in parents (e.g., B child impossible from two A/O parents).
• Validate options against tree: Only sequences fitting all constraints without impossible genotypes.

Why A is correct:

• Matches codominant inheritance where each numbered individual's blood group is possible from parental alleles (A/B/AB/O phenotypes align with Mendelian segregation).

Why the others are wrong:

• B includes invalid "C" blood group, which does not exist in ABO system.
• C omits a required individual or forces impossible B from non-B parents.
• D assigns O to a spot requiring A/B allele presence.

Final answer: A