Cita APA (7a ed.)

Abbs, B., & Freebairn, I. B. (2005). Sky 1: Student's book.

Cita Chicago Style (17a ed.)

Abbs, Brian, y Ingrid Bygrave Freebairn. Sky 1: Student's Book. Harlow, 2005.

Cita MLA (9a ed.)

Abbs, Brian, y Ingrid Bygrave Freebairn. Sky 1: Student's Book. 2005.