“INFUSING A GAMIFICATION MECHANISM THROUGH DUOLINGO FOR ENGLISH SPEAKING PROFICIENCY: PERCEPTIONS OF THE INDONESIAN EFL INSTRUCTOR AND STUDENTS”. Konstruktivisme : Jurnal Pendidikan Dan Pembelajaran, vol. 12, no. 1, Jan. 2020, pp. 69-80, https://doi.org/10.35457/konstruk.v12i1.894.