Cita APA (7th ed.)
Wallen, R. N. (1992). Introduction to physical geography. WM C. Brown.
Cita Chicago (17th ed.)
Wallen, Robert N. Introduction to Physical Geography. Boulevard: WM C. Brown, 1992.
Cita MLA (9th ed.)
Wallen, Robert N. Introduction to Physical Geography. WM C. Brown, 1992.
Atenció: Aquestes cites poden no estar 100% correctes.