In this case, since bacteria (A.) reproduce via asexual reproduction via mitosis and the animal (D.) and vegetal (C.) cells could reproduce via sexual or asexual reproduction depending on the organism, they do not need a host to start the replication of the DNA and therefore reproduce. In such a way, it is widely known that viruses need a host that facilitates the replication of their DNA or RNA (depending on the virus) since they only have their genetic information but they do not have neither the RNA nor the DNA polymerase that favor such process, that is why they need a host.
