8Mason, R.(1994). Using Communications Media for Open and Flexible Learning. London: Kogan Pages.
9Juler,P.A.(1990). Promoting interaction; maintaining independence: swallowing the mixture, Open Learning, vol.5, no.2,24-33.
10MaIsaac, M. S.and C. N. Gunawardena. (1996) Distance Education, handbook of research for educational communications and technology.Ed. D.H. Jonassen, 403-437. New York: Macmillan Library. Reference USA.
