Kaplan, R. D., & Dufris, W. (2017). Earning the Rockies: How geography shapes America's role in the world (Unabridged.). HighBridge Audio.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रKaplan, Robert D., और William Dufris. Earning the Rockies: How Geography Shapes America's Role in the World. Unabridged. Minneapolis, MN: HighBridge Audio, 2017.
एमएलए (8वां संस्करण) प्रशस्ति पत्रKaplan, Robert D., और William Dufris. Earning the Rockies: How Geography Shapes America's Role in the World. Unabridged. HighBridge Audio, 2017.
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