1. Apple: Website of iTunes U, Apple Inc. (2013),
http://www.apple.com/education/itunes-u
2. CC: Website of Creative Commons (2013),
http://creativecommons.org
3. CCOTC: Website of College Open Textbooks, Community College Open Textbooks Collaborative (2013),
http://www.collegeopentextbooks.org
4. CNX: Website of Connexions (2013),
http://www.cnx.org
5. CORE: Website of China Open Resources for Education (2013),
http://www.core.org.cn