Shapiro, Alan C.
Boston Allyn and Bacom 1986,
Buku Teks
Gibson, Charles H., author
South Western College , 2001
Buku Teks
Gibson, Charles H., author
PWS-KENT Publishing , 1989
Buku Teks
Gibson, Charles H., author
South-Western, 1992
Buku Teks
Hughes, Joan K., author
John Wiley & Sons, 1981
Buku Teks