Density/(密度) -> #3of3 Advanced/(深入) -> Properties of Sounds/(声音的属性) -> Learn/(学习)

Density/(密度) -> Properties of Sounds/(声音的属性) -> Theory/(理论) -> Step 1 Middle School/(第一步初中) -> Years Group/(年级群)

Density/(密度) -> Modes of Listening/(聆听模式) -> Theory/(理论) -> Step 2 High School/(第二步高中) -> Years Group/(年级群)

Density/(密度) -> Properties of Sounds/(声音的属性) -> #3of3 Advanced/(深入) -> #[Tier 6] Pedagogical Aspects for Children/([第六]教育层为儿童) -> Users Group/(用户群)