Billings, E., & Westmore, A. (1980). The Billings method of Natural Family Planning: Controlling fertility without drugs or devices (1st American ed.). Random House.
Citação do estilo Chicago (17ª ed.)Billings, Evelyn, e Ann Westmore. The Billings Method of Natural Family Planning: Controlling Fertility Without Drugs or Devices. 1st American ed. New York: Random House, 1980.
Citação MLA (8ª ed.)Billings, Evelyn, e Ann Westmore. The Billings Method of Natural Family Planning: Controlling Fertility Without Drugs or Devices. 1st American ed. Random House, 1980.
Nota: a formatação da citação pode não corresponder 100% ao definido pela respectiva norma.