Navaruttanaporn, Srijittra. 2021. “Developing the Instructional Self-learning Media of English Speaking Skills for Hotel Front Office Staff in Muang District, Loei Province”. Research and Development Journal, Loei Rajabhat University 16 (55):105-16. https://so05.tci-thaijo.org/index.php/researchjournal-lru/article/view/243744.