M. Hum, H. R., & Gultom, D. S. (2018). Increasing Students’ Understanding of the Simple Past Tense Using Discovery Learning at VII grade students of SMP Negeri 4 Doloksanggul in Academic Year 2017/218. International Journal of English Literature and Social Sciences, 3(5), 839–842. https://doi.org/10.22161/ijels.3.5.25