Verduin, J. R., & Clark, T. A. (1991). Distance education: The foundations of effective practice. Jossey-Bass.
Lua i Stíl Chicago (17ú heag.)Verduin, John R., agus Thomas A. Clark. Distance Education: The Foundations of Effective Practice. San Francisco: Jossey-Bass, 1991.
Lua MLA (8ú heag.)Verduin, John R., agus Thomas A. Clark. Distance Education: The Foundations of Effective Practice. Jossey-Bass, 1991.
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