Bingham, Neil, author
Page One Publishing , 2000
Buku Referensi
Davis, Gwenn
London : Mansell Publishing Limited, 1991,
Buku Referensi
Smith, Leslie, author
Macmillan, 1989
Buku Teks
Harcourt, Brace and company, 1950
Buku Teks
compiled by Ruth Z. Temple; edited by Martin Tucker
Frederick Ungar Publishing, 1981
Buku Referensi