Viruses are the microorganisms who needs to infect the living host cells, in order to replicate or reproduce. These infectious agents are capable of injecting and infecting all the life forms present, including the plants, animals and bacteria. The viruses were not among the first organisms to evolve as in order to replicate themselves and continue through the time they needed other organisms' cell.
Hence, the correct answer is 'viruses have to infect a living cell in order to reproduce'.
