Renandya, Willy A, Stephen Krashen, and George M Jacobs. 2018. “The Potential of Series Books: How Narrow Reading Leads to Advanced L2 Proficiency”. LEARN Journal: Language Education and Acquisition Research Network 11 (2):148-54. https://so04.tci-thaijo.org/index.php/LEARN/article/view/161631.