E. Simamora, Rustam, Dewi Rotua Sidabutar, and Edy Surya. 2017. “Improving Learning Activity and Students”. International Journal of Sciences: Basic and Applied Research (IJSBAR) 33 (2):321-31. https://www.gssrr.org/index.php/JournalOfBasicAndApplied/article/view/7368.