Gaya APA

Gabel, R, A., Sager, R, J. (1982). Essentials of physical geography (2nd ed.). Philadelphia: Saunders college Pub..

Gaya MLA

Gabel, Robert, A., Sager, Robert, J. "Essentials of physical geography". 2nd ed. Philadelphia: Saunders college Pub., 1982. Text.