Sinaga, P., A. Suhandi, and . Liliasari. “Improving the Ability of Writing Teaching Materials and Self-Regulation of Pre-Service Physics Teachers through Representational Approach”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 15, no. 1, Apr. 2014, pp. 80-94, https://gssrr.org/index.php/JournalOfBasicAndApplied/article/view/2084.