Whitney, N. (1984). Checkpoint: English 1 (1a. ed.). Oxford University.
Chicago Style (17th ed.) ZitazioaWhitney, Norman. Checkpoint: English 1. 1a. ed. Oxford: Oxford University, 1984.
MLA (9th ed.) ZitazioaWhitney, Norman. Checkpoint: English 1. 1a. ed. Oxford University, 1984.
Kontuz: berrikusi erreferentzia hauek erabili aurretik.