Matsuda, N. ., H. . Ogawa, T. . Hirashima, and H. . Taki. “A Generating Technique and Knowledge Representation of Multiple-Answer Problems for Learning With Solving Knowledge”. Research and Practice in Technology Enhanced Learning, vol. 10, June 2015, https://rptel.apsce.net/index.php/RPTEL/article/view/2015-10006.