$\begin{array}{1 1}\text{a.It is an application of biotechnology,in which a defective gene is manipulated by introduction of normal, healthy and functional gene} \\ \text{b.The genetic disorders that are being investigated for gene therapy, range from sickle cell anaemia to SCID} \\ \text{c.The first clinical gene therapy was given in 1990 to a four year old girl with adenosine deaminase deficiency (ADD)} \\\text{d.All of these} \end{array}$
