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Buku Teks
Martocchio, Joseph J., author
McGraw-Hill/Irwin, 2014
Buku Teks
Perrin, Towers, author
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Buku Referensi
The Brookings Institution, 1975
Buku Teks
edited by Christopher G. Reddick, Jerrell D. Coggburn
CRC Press, 2008
Buku Referensi