Answer: option A and B (AUC & AUU)
Explanation:
Codons of isoleucine are AUC and AUU, while codons of methionine are AUA and AUG.
Therefore, a single base change in cytosine of "AUC" could yeild any of methionine codons, also a single base change in AUU will do the same.
This single base change is refers to as point mutation, and it is generally reversible.
