Sikula, Andrew F.
Cal Wiley, 1976
Buku Teks
Strauss, George
Prentice-Hall, 1980
Buku Teks
Strauss, George
Prentice Hall of India, 1985
Buku Teks
Straus, George
Prentice-Hall, 1967
Buku Teks
Jackson, Susan E.
South Westh Western College, 2000
Buku Teks