Caifen, Wang, Fu Hailun, and Cao Rongrong. “The Research on Graduate Students’ Understanding of Three Basic Limit Concepts”. American Journal of Education and Learning 3, no. 2 (December 4, 2018): 100–107. Accessed November 22, 2024. https://onlinesciencepublishing.com/index.php/ajel/article/view/43.