Gaya APA

Gabler, R, E. et al (1994). Essentials of Physical Geography (update version) (Ed. 4). Orlando-Florida: Harcourt Brace College Publishers.

Gaya MLA

Gabler, Robert, E.. et al. "Essentials of Physical Geography (update version)". Ed. 4 Orlando-Florida: Harcourt Brace College Publishers, 1994. Text.