Answer:
b
Step-by-step explanation:
Human blood types show co-dominance. This means that both alleles A and B alleles are expressed (one is not dominant over the other). This means that an AB blood type exists. This is distinct from incomplete dominance, where the phenotype is a "blend" of the two. That means the third option is false.
There is more than one possible genotype for blood types A and B. An individual can be AA, or AO and still have an A blood type, and can be BB or BO and still have type B blood. That means the first option is false.
Blood type is controlled by a single gene (ABO) that has 3 alleles, so it is true that it is a trait that has multiple alleles.
The antibodies produced are in fact the opposite of the phenotype, the phenotype refers to the antigen produced, so the final option is false.
I have attached a table I think might help!