Gill, John
Paul Chapman Publishing, Inc, 1991
Buku Teks
Retno Wulandari
Fakultas Ekonomi dan Bisnis Universitas Indonesia, 1993
UI - Skripsi Membership
Zulfia Hanum Alfi Syahr
Research and Development Agency Ministry of Home Affairs, 2018
Artikel Jurnal
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Springer, 2007
Buku Teks
Gerstenfeld, Arthur
California Addison-Wesley Publishing , 1970
Buku Teks