1Childs,G.B.(1969):Recent research developments in correspondence instruction.In Proceedings of the eigth international conference of the ICCE.Paris[Z].
2Keegan,D.(1990):Foundations of distance education.2nd.ed.London:Routledge.p.44[Z].
3Garrison,D.R.(1989):Understanding distance education.A framework for the future.London:Routledge[Z].
4Holmberg,B.(1986):A Discipline of Distance Education.J.of Dist.Ed.1,1,24-40[Z].
5Baath,J.A.(1980):Postal Two-Way Communication in Cor respondence Education.Lund:Gleerup[Z].
6Jiang,M.and Ting,E.(2000).A study of factors influencing students'perceived learning in a web-based course environment.International Journal of Educational Telecommunications,6(4):317-338[Z].
7Coldeway,D.O.(1990):Concepts of Ex perimental I nquiry in Distance Education./A Systems Perspective0.ACSDE Research Monog raph 5,23-34.College Park:University of Pa[Z].
