The gene $I$ that controls the $ABO$ blood grouping produces antigens on the surface of red blood cells. What are these antigens made of?

If a child has $O$ type of blood group and the father has $B$ type,the genotype of the father will be:

$A$ couple has four children with blood groups $A, AB, A,$ and $O$ respectively. What are the genotypes of the parents' blood groups?

$A$ child has blood group $O$. If the father has blood group $A$ and mother has blood group $B$,work out the genotypes of the parents and the possible genotypes of the other offspring.

Inheritance of $ABO$ blood group system is an example of

The plasma membrane of the red blood cells has ...$A$... polymers that protrude from its surface and the kind of sugar is controlled by the gene. The gene $I$ has three alleles ...$B$... The alleles and produce a slightly different form of the sugars,while allele $i$ doesn't produce any ...$C$...
Choose the correct option for $A, B$ and $C$.