Widanta, IM. Rai Jaya, A.A. Raka Sitawati, IN. Rajin Aryana, and IW. Dana Ardika. 2016. “Learning Center With Self-Directed Learning: A Foundation for TOEFL Learning Activity”. International Journal of Linguistics, Literature and Culture 2 (4):64-71. https://sloap.org/journals/index.php/ijllc/article/view/139.