S, et al. “Guided Discovery-Blended Learning (GDBL) for Critical Thinking Skill Empowerment: A Learning Strategy in Human Excretory System ”. Biosfer: Jurnal Pendidikan Biologi, vol. 13, no. 2, Oct. 2020, pp. 266-79, doi:10.21009/biosferjpb.v13n2.266-279.