2Baath, J.A.. Postal Two-way Communication in Correspondence Education[J]. Epistolodidaktika 1980,(1): 1-2.
3Keegan, Desmond (1991). The Study of Distance Education:Terminology, Definition and the Field of Study[A]. In Holmberg B and Ortner G (eds). Research into Distance Education[C],Frankfurt am Main: Lang. 36-45.
4Holmberg, Berje (1989). Terminology and Epistemology: A Comment on Devlin's Analysis of Distance Education as a Discipline [DB/OL]. http://cade.icaap.org/vol4.1/10e_dialogue_3-holmberg.html, 2005-11-10.
1Keegan D . The study of distance education: terminology, definition and the field of study[A]. Holmberg B and Ormer G (eds) Research into distance education[C]. Frankfurt am Main: Lang, 1991.36-45.
