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Buku Referensi
Black, Geoff
Prentice-Hall, 2002
Buku Referensi
Black, Geoff
London : Prentice Hall, 2001,
Buku Referensi
Nurul Fatiha
Universitas Indonesia, 2007
UI - Tesis Membership
Rudi Bambang Trisilo
1987
UI - Skripsi Membership