H. Cadiao Philippines, Esperval Cezhar, and Ma. Joji B. Tan. “Effectiveness of Using a Flipped Classroom in Improving English Grammar Proficiency”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 51, no. 2, Apr. 2020, pp. 45-57, https://www.gssrr.org/JournalOfBasicAndApplied/article/view/10943.