Percil, J., & Gray, J. (1988). Prospects: An advanced course teacher's book. Penguin Books.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रPercil, John, और Joanna Gray. Prospects: An Advanced Course Teacher's Book. London: Penguin Books, 1988.
एमएलए (9वां संस्करण) प्रशस्ति पत्रPercil, John, और Joanna Gray. Prospects: An Advanced Course Teacher's Book. Penguin Books, 1988.
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