Spilker, Bert, author
Raven Press, 1984
Buku Teks
Cambridge Hobsons 1987
Buku Referensi
Lagerwey, Walter
U.S. Office of Education, 1964
Buku Referensi
Thornton, George C
Lawrence Erlbaum Associates, 2004
Buku Teks
Endres, Alfred, author
[Springer, ], 2012
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