APA (7th ed.) Zitazioa
Graham, B. (1975). Angels: God's secret agents. Doubleday.
Chicago Style (17th ed.) Zitazioa
Graham, Billy. Angels: God's Secret Agents. Garden City, N.Y.: Doubleday, 1975.
MLA (9th ed.) Zitazioa
Graham, Billy. Angels: God's Secret Agents. Doubleday, 1975.
Kontuz: berrikusi erreferentzia hauek erabili aurretik.