The third codon (three bases) in the sequence was mutated from GAT to AAT. The GAT codon translates to the amino acid aspartic acid. The AAT codon translates to the amino acid asparagine. This is what's called a point mutation, specifically a missense mutation since the translated amino acid is changed. Deletion and inversion mutations are not the answer because these mutations involve the chromosomes as a whole, not just bases. Frame shift mutations occur when 1 or 2 (but not 3) bases are added or deleted from the sequence causing an array of point mutations (domino effect).
