Citazione Stile APA (7a Edizione)

Helgren, D. M., & Sager, R. J. (1995). World geography today. Holt, Rinehart and Winston.

Citazione stile Chigago Style (17a edizione)

Helgren, David M., e Robert J. Sager. World Geography Today. Austin, TX: Holt, Rinehart and Winston, 1995.

Citatione MLA (9a ed.)

Helgren, David M., e Robert J. Sager. World Geography Today. Holt, Rinehart and Winston, 1995.