Siahaan, Basar Lolo. 2019. “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 (1):49-61. https://ejournal.uhn.ac.id/index.php/jetafl/article/view/116.