Wu, Shaoqun, Ian H. Witten, Arthur Walter Edwards, David M. Nichols, and Raúl Aquino. “A Digital Library of Language Learning Exercises”. International Journal of Emerging Technologies in Learning (iJET) 2, no. 1 (July 18, 2006). Accessed March 29, 2024. https://online-journals.org/index.php/i-jet/article/view/15.