Kittson, E. Creagh
Milford, 1926
Buku Teks
Ur, Penny, author
Cambridge University Press, 1991
Buku Teks
Rivers, Wilga M., author
Cambridge University Press, 1994
Buku Teks
Chastain, Kenneth
Rand McNally , 1971
Buku Teks
Ur, Penny, author
Cambridge University Press, 2006
Buku Teks