On a molecular level (i.e., in terms of the actual molecules or monomers), how does the HbA allele differ from the HbS allele?
a) The HbA allele contains a substitution of adenine for thymine.
b) The HbA allele contains a substitution of cytosine for guanine.
c) The HbA allele contains a substitution of adenine for cytosine.
d) The HbA allele contains a substitution of thymine for adenine.