Answer:
Option (A).
Step-by-step explanation:
Gene therapy may be defined as the type of therapeutic medicine used to treat the genetic problems of the individual. The genetic therapy was first discovered by Martin Cline.
In the genetic therapy, the defective copy of a gene is replaced by the function copy of gene. The gene can be inserted directly by the injections or by using any retrovirus.
Thus, the correct option is (A).