Answer:
C.] A—C—T—G—C—G—A—T
Step-by-step explanation:
In option A the last base is substituted with U, thus this is a substitution, not an insertion.
In option B the fourth base G is not present. There is one less base, thus this is a deletion, not an insertion.
In option D the base sequence is the same as the normal nucleotide sequence.