Balbach, Margaret
Brace Jovanovich College, 1991
Buku Teks
Cooper, Melanie M.
McGraw-Hill, 2009
Buku Teks SO
Scheinfein, Michael
Kendall/Hunt, 1993
Buku Teks SO
Gerking, Shelby D.
Burgess, 1970
Buku Teks
Patterson, C.O. Pat
Burgess Publishing , 1973
Buku Teks