Cita APA (7th ed.)

English Languaje Services. (1964). The Key to english. Collier Macmillan.

Cita Chicago (17th ed.)

English Languaje Services. The Key to English. London: Collier Macmillan, 1964.

Cita MLA (9th ed.)

English Languaje Services. The Key to English. Collier Macmillan, 1964.