Study the following step which are followed during the process of gene therapy while treating a patient of SCID
(i) Retrovirus infects lymphocytes extracted from bone marrow of the patient and cultured
(ii) Engineered cells are injected into patient's bone marrow
(iii) Normal allele is inserted into a retrovirus
(iv) Retrovirus makes a DNA copy of its RNA. This DNA carrying the normal allele gets inserted into the chromosome of the host cell
Arrangement the above given steps in correct sequence and select the correct option