Billings, E., & Westmore, A. (1980). The Billings method of Natural Family Planning: Controlling fertility without drugs or devices (1st American ed.). Random House.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रBillings, Evelyn, और Ann Westmore. The Billings Method of Natural Family Planning: Controlling Fertility Without Drugs or Devices. 1st American ed. New York: Random House, 1980.
एमएलए (8वां संस्करण) प्रशस्ति पत्रBillings, Evelyn, और Ann Westmore. The Billings Method of Natural Family Planning: Controlling Fertility Without Drugs or Devices. 1st American ed. Random House, 1980.
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