Roebuck, Deborah Britt
Business Expert Press, 2012
Buku Teks
Munter, Mary
Prentice-Hall, 1982
Buku Referensi
Veech, Annette M.
Prentice-Hall, 2002
Buku Teks
Ewald, Helen Rothschild
Prentice-Hall International, 1997
Buku Teks
Machin, John L.J.
McGraw-Hill, 1980
Buku Teks