Siahaan, Basar Lolo. “Effect of Group Work Strategy to the Speaking Achievement of Second Semester Students of English Study Program at University of HKBP Nommensen Pematangsiantar”. Journal of English Teaching as a Foreign Language 5, no. 1 (June 30, 2019): 49-61. Accessed May 19, 2024. https://ejournal.uhn.ac.id/index.php/jetafl/article/view/116.