Human immunodeficiency virus belongs to the family of retroviruses. What is the most characteristic trait of this family of viruses?

Answer options

1. Radioimmunoassay is needed for antigen detection
2. The presence of reverse transcriptase enzyme
3. Nucleic acid is not Integrated into the genome of the host
4. Enzyme-linked immunosorbent assay is needed for antigen detection
5. These are simple viruses that affect only humans