Barbara Robinson. (1998). Focus: Interactive grammar for students of ESL. Cambridge, UK: Cambridge Univ. Press.
Chicago Style aipamenaBarbara Robinson. Focus: Interactive Grammar for Students of ESL. Cambridge, UK: Cambridge Univ. Press, 1998.
MLA aipamenaBarbara Robinson. Focus: Interactive Grammar for Students of ESL. Cambridge, UK: Cambridge Univ. Press, 1998.
Kontuz: berrikusi erreferentzia hauek erabili aurretik.