Levinson, Nan
[American Management Association;, ], 2000
eBooks
Ries, Al
McGraw-Hill, 1986
Buku Teks SO
Griya Ratri Putri
Fakultas Ilmu Sosial dan Ilmu Politik Universitas Indonesia, 2012
UI - Skripsi Open
Time Warner, 2005
Buku Teks SO
Manktelow, James
Signal House, 2004
Buku Teks