The news provided by the military to soldiers serving in Vietnam was sometimes censored. Thirsting for uncensored news and music, ambitious GIs put to use the abundance of available communications equipment and became Vietnam's underground radio pirates. The pirate stations used military communications equipment instead of commercial broadcast equipment to pass along advice, information, and support not communicated by upper echelon military personnel. Soldiers in the field could hear the broadcasts on their field radios. This would be an example of a(n) ____ communication channel. a. downward b. upward c. horizontal d. formal e. informal