Powell, D., Walker, E., & Elsworth, S. (2008). Grammar Practice for Upper Intermediate Students: With key (Third Edition.). Pearson Education Limited.
Citace podle Chicago (17th ed.)Powell, Debra, Elaine Walker, a Steve Elsworth. Grammar Practice for Upper Intermediate Students: With Key. Third Edition. Essex, England: Pearson Education Limited, 2008.
Citace podle MLA (9th ed.)Powell, Debra, et al. Grammar Practice for Upper Intermediate Students: With Key. Third Edition. Pearson Education Limited, 2008.
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