Artikel Jurnal
Garner, Helen, author
Penguin Books, 1967.
Buku Teks
Richardson, Henry Handel, author
William Heinemann, 1977
Buku Teks
Payne, James, author
Illinois National Textbook, 1994
Buku Teks
Olsen, Gary, author
Ohio North Light Books , 1997
Buku Teks