1. Analyzing the costs and benefits of multi-representational learning environments;Ainsworth,1998
2. Allen, I. E., & Seaman, J. (2005). Growing by degrees: Online education in the United States, 2005. The Sloan Consortium. http://www.sloan-c.org/resources/growing_by_degrees.pdf.
3. Human memory: Theory and practice;Baddeley,1997
4. Flexibly structuring the interaction in a CSCL environment;Baker,1996
5. The knowledge integration environment: Theory and design;Bell,1995