8E Henri, Computer conferencing and content analysis [A]. In A. Kaye (Ed.), Collaborative Learning Through Computer Conferencing [C]. Berlin: Springer-Verlag, 1991, pp. 117-136.
9E. Stacey, "Social presencoonline: Net= working learners at a distance". Education and Infor- mation Technologies, 2002,7 (4): 287-294.