Saadah, R., H. Hastuti, and S. Sudarmaji. “The Correlation of Sentence Mastery and Learning Motivation With Service Letter Writing Skills”. IJLHE: International Journal of Language, Humanities, and Education, vol. 2, no. 2, Dec. 2019, pp. 32-40, https://jurnal.stkippgribl.ac.id/index.php/ijlhe/article/view/840.