Perwira, Susilo Adi. “Textbook Readibility Assessment of K13 English Textbook For Twelfth Grade”. IJET (Indonesian Journal of English Teaching) 8, no. 2 (December 31, 2019): 38–47. Accessed April 23, 2024. https://jurnalftk.uinsby.ac.id/index.php/IJET/article/view/212.