Powell, D., Walker, E., & Elsworth, S. (2008). Grammar Practice for Upper Intermediate Students: With key (Third Edition.). Pearson Education Limited.
Chicago-Zitierstil (17. Ausg.)Powell, Debra, Elaine Walker, und Steve Elsworth. Grammar Practice for Upper Intermediate Students: With Key. Third Edition. Essex, England: Pearson Education Limited, 2008.
MLA-Zitierstil (9. Ausg.)Powell, Debra, et al. Grammar Practice for Upper Intermediate Students: With Key. Third Edition. Pearson Education Limited, 2008.
Achtung: Diese Zitate sind unter Umständen nicht zu 100% korrekt.