Cita APA (7th ed.)

Langan, J., & Butcher, P. A. (2001). English Skills (séptima edición.). McGraw - Hill Companies, Inc.

Cita Chicago (17th ed.)

Langan, John, i Phillip A. Butcher. English Skills. séptima edición. New York, NY: McGraw - Hill Companies, Inc, 2001.

Cita MLA (9th ed.)

Langan, John, i Phillip A. Butcher. English Skills. séptima edición. McGraw - Hill Companies, Inc, 2001.