Cita APA (7th ed.)
Helgren, D. M., Sager, R. J., & Israel, S. (1985). World geography today. Holt, Rinehart and Winston.
Cita Chicago (17th ed.)
Helgren, David M., Robert J. Sager, i Saul Israel. World Geography Today. New York: Holt, Rinehart and Winston, 1985.
Cita MLA (9th ed.)
Helgren, David M., et al. World Geography Today. Holt, Rinehart and Winston, 1985.
Atenció: Aquestes cites poden no estar 100% correctes.