Schwartz, Robert J.
Crowell , 1955
Buku Referensi
Paxton, John
J.M. Dent & Sons, 1992
Buku Referensi
Jones, David J.
Second Back Row Press, 1981
Buku Teks
Jones, David J.
Australia, Second Back Row Press
Buku Referensi
Merriam-Webster, 1985
Buku Referensi