Cita APA (7a ed.)

Kirby, S., & Key, P. (1989). Penguin elementary speaking skills: Student's book. Penguin Books.

Cita Chicago Style (17a ed.)

Kirby, Stephen, y Patty Key. Penguin Elementary Speaking Skills: Student's Book. London: Penguin Books, 1989.

Cita MLA (9a ed.)

Kirby, Stephen, y Patty Key. Penguin Elementary Speaking Skills: Student's Book. Penguin Books, 1989.