Snowman, Jack
Wadsworth and Cengage Learning, 2012
Buku Teks
Kolb, David A.
Prentice-Hall, 1974
Buku Teks
Nicolson, Paula
MacMillan Education, 1986
Buku Teks SO
Gilmer, B. von Haller (Beverly von Haller), 1909-1994
McGraw-Hill, 1967
Buku Teks SO
Wilson, John A.R.
McGraw-Hill, 1974
Buku Teks