A true reversion occurs when the wild-type DNA sequence is restored to encode its original message by a second mutation at the same site or within the same codon. Which of the following isoleucine codon(s) could be mutated once to form a methionine codon, and then mutated at a second site to restore an isoleucine codon?
A. AUC.
B. AUU.
C. AUA.
D. None of these codons.