| URL | Title | Id |
|---|---|---|
| http://digfir-published.macmillanusa.com/astro_interactive_exercise/ie_comets.html | Chapter 1. Comets | 513b9fe7b11c0f915f000001 |
| http://digfir-published.macmillanusa.com/astro_interactive_exercise/ie_comets_dlap.xml | DLAP questions | 513b9fe7b11c0f915f000001 |