c. a virus
Work Step by Step
Viruses can either contain DNA or RNA as their means of transmitting their genetic material. When the virus attaches to a host cell, it injects its genetic material, either DNA or RNA, into the cell. In the case of DNA viruses, the virus causes the cell to replicate the viral DNA and assemble more copies of the virus. With an RNA virus, the RNA injected into the cell must be changed into DNA first before more viruses can be made. Although RNA viruses incorporate this extra step to replicate themselves, viral infections from RNA viruses are more difficult to treat than diseases caused by DNA viruses.