Lubis, Nina, and L Lufri. 2022. “Development Of Student’s Activity Sheet (SAS) Based On Problem-Solving About Digestive System Materials In Humans In Class XI SMAN 1 Panyabungan Selatan”. PENBIOS: JURNAL PENDIDIKAN BIOLOGI DAN SAINS 6 (02), 51-58. https://doi.org/10.51673/penbios.v6i02.832.