OBrien, Jack
Kiplinger Books, 1999
Buku Teks SO
Longman, 1999
Buku Teks
editors, Fred M. Cox ... [and others]
F.E. Peacock, 1977
Buku Teks SO
Wilcox, Dennis L.
Pearson Education, 2003
Buku Teks SO
edited by John E. Tropman, John L. Erlich, Jack Rothman
F.E.Peacock, 1995
Buku Teks SO