Butterfield, J. (2010). Verbal communication. Course Technology, Cengage Learning.
Citazione stile Chigago Style (17a edizione)Butterfield, Jeff. Verbal Communication. Australia: Course Technology, Cengage Learning, 2010.
Citatione MLA (9a ed.)Butterfield, Jeff. Verbal Communication. Course Technology, Cengage Learning, 2010.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.