[1] H. R. M. Hum and D. S. Gultom, “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,” IJELS, vol. 3, no. 5, pp. 839–842, 2018, doi: 10.22161/ijels.3.5.25.