An unusual sight in the Old West was the medicine show wagon . * Action or Linking

linking verb

It has was in the sentence

Difference Between an Action Verb and a Linking Verb? ... In order to tell the difference, you have to pay attention to how each type of verb is used in a sentence—linking verbs are used for descriptions, whereas action verbs tell you what someone (or something) is doing.

answer: b (host)

viruses use the cells of living organisms to reproduce. the cell which is used by virus is called as "host cell". it is a living cell in which virus multiplies, example bacteria, plant or an animal cell.

in this, the virus is a parasite, which uses host cell for its benefit (reproduction) by using the cell machinary of host cell.

it provides a unique and personal perspective on a significant historical event.