Answer: A could be a human; B could be a virus; C could be the nose; D could be the mucus membranes of the eyes
Step-by-step explanation:
In relation to infections by viruses, humans could be the host that the virus infects and grows in like the coronavirus. Viruses can enter into the body via the mucus membranes in the eyes especially when we touch them with our hands if our hands have come into contact with a virus.
After the virus has replicated in large enough numbers and spread to other parts of the body, we are able to infect others through portals of exit such as the nose and the mouth when we sneeze.