Christopherson, R. W. (1994). Geosystems: An introduction to physical Geography (2nd ed.). Macmillan.
Lua i Stíl Chicago (17ú heag.)Christopherson, Robert W. Geosystems: An Introduction to Physical Geography. 2nd ed. Englewood Cliffs: Macmillan, 1994.
Lua MLA (9ú heag.)Christopherson, Robert W. Geosystems: An Introduction to Physical Geography. 2nd ed. Macmillan, 1994.
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