APA

Keegan D., . (1993). Theoretical Principles of Distance Education. : Routledge.

Chicago

Keegan Desmond, . 1993. Theoretical Principles of Distance Education. : Routledge.

Harvard

Keegan D., . (1993). Theoretical Principles of Distance Education. : Routledge.

MLA

Keegan Desmond, . Theoretical Principles of Distance Education. : Routledge. 1993.