Roji, F., D. Basya, and F. Al - Fauzi. “The Application of Multimedia Based Zello Walkie Talkie in Improving First Grade Students’ Speaking Skill at SMK Kesehatan Medika Farma”. Jurnal Educazione : Jurnal Pendidikan, Pembelajaran Dan Bimbingan Dan Konseling, vol. 6, no. 1, May 2018, pp. 24-30, https://ejurnal.uij.ac.id/index.php/EDU/article/view/568.