This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics, Subject name: Pathology
Retrovirus is used for gene therapy because - 
Select and explain. 
A. They have sequences common to human genome, B. They integrate rapidly into human genome, C. Economically viable, D. Easy to perform in labs
B: They integrate rapidly into human genome
Answer: B: They integrate rapidly into human genome 
Explanation: 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