Here we are comparing the DNA sequence of the gene for skin pigment in a normal gorilla (sample 1) and an albino gorilla (sample 2).
The sequences are the following:
Sample 1
ATT ACA GTA CTG GCA
Sample 2
ATT ACA ATA CTG GGC A
We can see that the sequences have different lengths, sample 1 has a length of 15 base pairs (bp), while sample 2 has 16 bp. This means there is an extra nucleotide, so this is an insertion mutation.
This means the correct answer is C. Insertion