Hays, S. P. (1999). Conservation and the gospel of efficiency: The progressive conservation movement, 1890-1920. University of Pittsburgh Press.
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Chicago-čujuhus (17. p.)
Hays, Samuel P. Conservation and the Gospel of Efficiency: The Progressive Conservation Movement, 1890-1920. Pittsburgh, Pennsylvania: University of Pittsburgh Press, 1999.
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MLA-čujuhus (9. p.)
Hays, Samuel P. Conservation and the Gospel of Efficiency: The Progressive Conservation Movement, 1890-1920. University of Pittsburgh Press, 1999.
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