Polley, R. L. (1965). Herbert Hoover's: Challenge to America. His life and words (1a. ed.). Country Beautiful Foundation.
Chicago-čujuhus (17. p.)Polley, Robert L. Herbert Hoover's: Challenge to America. His Life and Words. 1a. ed. Nueva York: Country Beautiful Foundation, 1965.
MLA-čujuhus (9. p.)Polley, Robert L. Herbert Hoover's: Challenge to America. His Life and Words. 1a. ed. Country Beautiful Foundation, 1965.
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