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 cod on. 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? Select all that apply. (Note that two different positions in the codon must be mutated.)

AUC
AUU
AUA
none of these codons