Diningrat, S. W. M., P. Setyosari, S. Ulfa, and U. Widiati. “Integrating PBI in the Flipped Classroom: A Framework for Effective Instruction”. World Journal on Educational Technology: Current Issues, vol. 12, no. 2, Apr. 2020, pp. 117-2, doi:10.18844/wjet.v12i2.4662.