Jones, L. (1986). Progress to Proficiency: Student's Book. Cambridge: Cambridge University.
Chicago Style aipamenaJones, Leo. Progress to Proficiency: Student's Book. Cambridge: Cambridge University, 1986.
MLA aipamenaJones, Leo. Progress to Proficiency: Student's Book. Cambridge: Cambridge University, 1986.
Kontuz: berrikusi erreferentzia hauek erabili aurretik.