Cita APA (7a ed.)

Ryall, R. J. (1973). The digestive system. Penguin Education.

Cita Chicago Style (17a ed.)

Ryall, R. J. The Digestive System. Harmondsworth: Penguin Education, 1973.

Cita MLA (9a ed.)

Ryall, R. J. The Digestive System. Penguin Education, 1973.