Widanta, I. R. J., Sitawati, A. R., Aryana, I. R., & Ardika, I. D. (2016). Learning center with self-directed learning: a foundation for TOEFL learning activity. International Journal of Linguistics, Literature and Culture, 2(4), 64–71. Retrieved from https://sloap.org/journals/index.php/ijllc/article/view/139