Nugraha, D. N. S., E. C. M. Simatupang, P. Sari, H. Gunawan, D. Dianita, and S. Rusyan. “Duolingo As an Artificial Intelligence Technology-Based Learning System in English”. Jurnal Sinestesia, vol. 13, no. 2, Sept. 2023, pp. 1085-9, https://www.sinestesia.pustaka.my.id/journal/article/view/419.