Doff, A., & Jones, C. (1997). Language in use: Upper-intermediate : self-study workbook with answer key (1st print.). Cambridge University Press.

Doff, Adrian, and Christopher Jones. Language in Use: Upper-intermediate : Self-study Workbook with Answer Key. 1st print. Cambridge: Cambridge University Press, 1997.

Doff, Adrian, and Christopher Jones. Language in Use: Upper-intermediate : Self-study Workbook with Answer Key. 1st print. Cambridge University Press, 1997.