Cita APA (7a ed.)

Walker, E., & Elsworth, S. (1994). Grammar practice for intermediate students (Rev. ed.). Longman.

Cita Chicago Style (17a ed.)

Walker, Elaine, y Steve Elsworth. Grammar Practice for Intermediate Students. Rev. ed. Essex: Longman, 1994.

Cita MLA (9a ed.)

Walker, Elaine, y Steve Elsworth. Grammar Practice for Intermediate Students. Rev. ed. Longman, 1994.