Doff, A., & Jones, C. (1997). Language in use: Upper-intermediate : classroom book (6th print.). Cambridge University Press.

Doff, Adrian, and Christopher Jones. Language in Use: Upper-intermediate : Classroom Book. 6th print. Cambridge: Cambridge University Press, 1997.

Doff, Adrian, and Christopher Jones. Language in Use: Upper-intermediate : Classroom Book. 6th print. Cambridge University Press, 1997.