$ABO$ blood group is a good example of:

In a family,the father has blood group '$A$' and the mother has blood group '$B$'. If the probability of their offspring having blood group '$AB$' is $50\%$,this indicates that:

If the mother's blood group is $B$ and the father's is $A$,what blood group$(s)$ can their offspring have?

Where are multiple alleles found?

What are alleles?

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 $C$.