<prompt> Retrovirus is used for gene therapy because -They have sequences common to human genomeThey integrate rapidly into human genomeEconomically viableEasy to perform in labs  <response>: Ans. is b they integrate rapidly into human gene In gene therapy vector is an agent required to transfer gene to an appropriate cell.Vectors used in gene therapy are of two types:Retrovirus belong to the vectors which integrate completely in the host chromosome.Other viruses used as vectors in gene therapy. Lenti virus - fully integrated Adeno virus - as episomes 