Pham, T. X. T., & Phan, V. H. (2011). An investigation into refusal strategies to requests by American speakers of English and Vietnamese learners of English. Đà Nẵng: The University of Da Nang.

Pham, Thi Xuan Thao., và Văn Hoà Phan. An Investigation Into Refusal Strategies to Requests By American Speakers of English and Vietnamese Learners of English. Đà Nẵng: The University of Da Nang, 2011.

Pham, Thi Xuan Thao., và Văn Hoà Phan. An Investigation Into Refusal Strategies to Requests By American Speakers of English and Vietnamese Learners of English. Đà Nẵng: The University of Da Nang, 2011.