July, Robert W
Charles Scribner's, 1970
Buku Teks
De Blij, Harm J., author
Northwestern University Press, 1968
Buku Teks
Standing, T. G.
Longmans, Green and Co., 1951
Buku Teks
Kennedy, Scott
Charles Scribner's , 1973
Buku Teks
Potter, Joan
Kensington Publishing, 2002
Buku Teks