May, John D.
Duxbury Press, 1972
Buku Teks
Junker, Buford H., author
University of Chicago Press, 1960
Buku Teks
Harrison, Brigid C., author
Thomson, 2008
Buku Teks
Blackman, Sheldon, author
John Wiley & Sons, 1971
Buku Teks
Townsend, John C., author
McGraw-Hill , 1953
Buku Teks