Cita APA (7th ed.)

Powell, D., Walker, E., & Elsworth, S. (2008). Grammar Practice for Upper Intermediate Students: With key (Third Edition.). Pearson Education Limited.

Cita Chicago (17th ed.)

Powell, Debra, Elaine Walker, i Steve Elsworth. Grammar Practice for Upper Intermediate Students: With Key. Third Edition. Essex, England: Pearson Education Limited, 2008.

Cita MLA (9th ed.)

Powell, Debra, et al. Grammar Practice for Upper Intermediate Students: With Key. Third Edition. Pearson Education Limited, 2008.