Piyamat, B., and K. . Deekawong. “Phonological Variations and Problems in English Pronunciation among Thai EFL Learners:: A Case Study of Undergraduate Students at Huachiew Chalermprakiet University”. Academic and Research Journal of Liberal Arts (Online), vol. 16, no. 1, June 2021, pp. 70-84, https://so04.tci-thaijo.org/index.php/larhcu/article/view/248822.