Which of the following do you think contributed the most to the success of Rhys’ gene therapy?

a.Rhys’ illness was never severe or life-threatening.
b.Rhys was very young at the time of the gene therapy procedure.,
c.Doctors were able to supplement his gene therapy with numerous rounds of bone marrow transplants.
d.Doctors were replacing only one gene, and they only had to insert that gene into bone marrow cells.