(1999). The Life force: Facing challenges. National Textbook Co.
Chicago Style aipamenaThe Life Force: Facing Challenges. Lincolnwood, Ill: National Textbook Co, 1999.
MLA aipamenaThe Life Force: Facing Challenges. National Textbook Co, 1999.
Kontuz: berrikusi erreferentzia hauek erabili aurretik.