Answer:
D. mutation.
Step-by-step explanation:
The substitution of one nucleotide base (such as C instead of T) for another is mutation.
Mutation represents a change in the genome or genetic material (in form of DNA sequence) of an organism.
Each DNA has its own sequence which are important to be kept constant when copies are being made during replication.
When a portion of a sequence in the DNA is deleted, substituted, inverted or repeated due to an error during replication, this can have a serious effect on the protein that will be translated during gene expression. Such DNA is said to have mutated.
The correct option is D