Lua APA (7ú heag.)
Ruffin, R. J., & Gregory, P. R. (1990). Principles of economics (4th ed.). Scott, Foresman.
Lua i Stíl Chicago (17ú heag.)
Ruffin, Roy J., agus Paul R. Gregory. Principles of Economics. 4th ed. Glenview, Illinos: Scott, Foresman, 1990.
Lua MLA (9ú heag.)
Ruffin, Roy J., agus Paul R. Gregory. Principles of Economics. 4th ed. Scott, Foresman, 1990.
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