The World Publishing Company, 1943
Buku Referensi
Macmillan, 1996
Buku Referensi
Mager, N.H., author
William Morrow and Co., 1982
Buku Referensi
Brewton
Laidlaw Brothers, 1958
Buku Teks
Murphy, Raymond, author
Cambridge University Press, 1998
Buku Teks