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 is b,

"the tracer looks harmless in flight, but the pilot’s bitten lips and white knuckles suggest how dangerous it can be."

it was correct.