As viruses cannot reproduce by themselves, they depend on the host cells that they infect to reproduce
Portals of entry are the sites where micro-organisms can enter a host and reproduce, causing diseases or infections. There are various portals of entry in the human body. This can include the skin, our mucous membranes, and even our respiratory and gastrointestinal tracts. Portals of exit are where these micro-organisms leave and spread to other individuals. Portals of exit include coughing, sneezing, and some of our bodily fluids.
I think the answer is c but I looked it up and got this: system or thing used as an example to follow or imitate.
