Robson, Wendy, author
Pearson Education , 1997
Buku Teks
O`Brien, James A., 1936-, author
McGraw-Hill, 2002
Buku Teks
Peppers, Don, author
John Wiley & Sons, 2011
Buku Teks
White, Andrew, author
Facet Publishing, 2006
Buku Teks
Saunders, E. Dale
University of Pennsylvania, 1964
Buku Teks