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Buku Teks
Gilbert, Alan, author
University Press, 1989
Buku Teks
editor, Everett M. Rogers; penerjemah: Dasmar Nurdin
LP3ES , 1989
Buku Teks
Melkote, Srinivas
Newbury Park, Calif. : Sage Publications,, 1991
Buku Teks
Penguin Books, 1978
Buku Teks