Stevenson, Burton, author
New York, Harper & Brothers
Buku Referensi
Berman, Alan
FrancesLincoln limited, 1997
Buku Teks
edited by L. Edward Purcell
Prentice-Hall, 1991
Buku Referensi
Ewen, David, author
Prentice-Hall, 1989
Buku Referensi
Ewen, David, author
Prentice-Hall, 1952
Buku Teks