Gene therapy, which includes the correction of defective genes, is a significant part of the human genome project. Which of these is an application of the technique?
A: A new protein, which can repair defective genes, is injected.
B: Mutated DNA sequences, which can pair with existing genes, are introduced.
C: The DNA sequences of the entire genomes of disease-causing microbes are compared.
D: A new gene, which codes for the protein that can repair defective genes, is introduced.