Answer:
The answer is D- gene added to bone marrow improves immune system function.
Step-by-step explanation:
Recently instead of using drugs or going for surgery, gene therapy is being used. Gene therapy is a technique of preventing or treating a disease by adding the gene. For example if there is a mutated gene responsible for causing a disease, it can be replaced by healthy gene using gene therapy. At times we can introduce new gene which may help the patient fight disease, or we can also knockout the mutated gene which is not functioning properly.