Zellmer, D. (1999). The spectator: A World War II bomber pilot's journal of the artist as warrior. Praeger.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रZellmer, David. The Spectator: A World War II Bomber Pilot's Journal of the Artist as Warrior. Westport, Conn.: Praeger, 1999.
एमएलए (9वां संस्करण) प्रशस्ति पत्रZellmer, David. The Spectator: A World War II Bomber Pilot's Journal of the Artist as Warrior. Praeger, 1999.
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