5Cass G. Gentry, Educational Technoloby -A Question of Meaning,Gary J. Anglin (1991), Instructional Technology -Past, Present, and Future,Englewood, Colorado, Libraries Unlimited, INC.
6Robert Heinich, The Proper Study of Instructional Technology, Gary J. Anglin(1991 ), Instructional Technology- Past, Present, and Future, Englewood, Colorado, Libraries Unlimited. INC.