Which one of the following vectors is used to replace the defective gene in gene therapy?

Genes are inserted into a person's cells and tissues to treat disease by replacing the defective gene. Viral vectors like adenoviruses and retroviruses are generally used to deliver the normal gene.  Adenovirus vectors can be replication-defective; certain essential viral genes are deleted and replaced by a cassette that expresses a foreign therapeutic gene. Such vectors are used for gene therapy, as vaccines, and for cancer therapy.