| URL | Title | Id |
|---|---|---|
| http://digfir-published.macmillanusa.com/astro_interactive_exercise/ie_star_formation_in_the_density-wave_model.html | Chapter 1. Star Formation in the Density-Wave Model | 514138c4b11c0ff21a00000c |
| http://digfir-published.macmillanusa.com/astro_interactive_exercise/ie_star_formation_in_the_density-wave_model_dlap.xml | DLAP questions | 514138c4b11c0ff21a00000c |