Leland, J., & Petkoff, R. (2018). Happiness is a choice you make: Lessons from a year among the oldest old (Unabridged.). Macmillan Audio.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रLeland, John, और Robert Petkoff. Happiness Is a Choice You Make: Lessons from a Year Among the Oldest Old. Unabridged. New York, NY: Macmillan Audio, 2018.
एमएलए (8वां संस्करण) प्रशस्ति पत्रLeland, John, और Robert Petkoff. Happiness Is a Choice You Make: Lessons from a Year Among the Oldest Old. Unabridged. Macmillan Audio, 2018.
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